What we know:
- A truck drove into a crowd of people on the busy Stockholm shopping street Drottninggatan just before 15:00 on Friday.
- Four people were killed and at least 15 injured.
- Police could not confirm reports of shots being fired near the Åhlens City department store or in the city's Fridhemsplan district.
- Police have said they have arrested a person in Märsta, north of Stockholm, who could be linked to the attack. They have confirmed that the person matches an image released by police earlier on Friday, but declined to release more details.
- Swedish brewery company Spendrups, which owns the truck, said it had been stolen earlier in the day.
- The city's subway system has resumed after being shut down, but some stations remain closed. Stockholm's central railway station was evacuated earlier in the day.
- Swedish PM Stefan Löfven has said that Sweden "has been attacked" in an apparent terrorist incident.
- The Prime Minister said Sweden was strengthening its borders after the attack.
- Police have made one arrest but are as yet unsure if the man being held was involved in the attack.
22:09 We are now closing the live report. Here is how the day's events unfolded:
21:51: Prime Minister Stefan Löfven told reporters on Friday evening that Sweden had reinforced its borders with immediate effect.
21:48: The Prime Minister said the attack was a "tragedy for the families involved." He stressed that Sweden would do "whatever it takes" for people to feel safe. "Terrorists want us to be afraid...to not live our lives normally, but that is what we are going to do. Terrorists can never defeat Sweden, never."
21:43: "A whole country is united in grief, anger and resolve," said Prime Minister Stefan Löfven at a Friday evening press conference.
21:34: When asked by a journalist at the press conference police said they have not been able to confirm reports of shootings near an Åhlens store and in Fridhemsplan.
21:27: Police declined to release more details about the identity of the person seized in Märsta, including their nationality.
21:22: "We have arrested a person who is of interest to us. We also released an image of a person we were looking for. The person arrested matches this description," Jan Evensson of the Stockholm Police said at a press conference on Friday night.
20:46 Faisal Khan, a Swedish citizen originally from Afghanistan, told The Local he was “pretty shaken up” after witnessing the incident at close quarters.
“Luckily he was not a good driver. It felt to me like he did not have experience driving such a large vehicle. This guy really wanted to cause a lot of damage.”
20:43: "One person has been arrested who could be linked to the matter. We cannot say more about the arrest right now," an update on the Stockholm Police website says.
20:40: Stockholm Police have confirmed that four people are dead and 15 people have been injured in the attack.
20:33: The Aftonbladet tabloid reports, citing several unnamed sources, that a man has been arrested in Märsta north of Stockholm. The reports are unconfirmed by police. Aftonbladet writes that the man had minor injuries and said he was guilty of the attack in Stockholm.
20:31: Stockholm County Council has confirmed that one person has died in hospital and 15 other injured people are being treated in relation to the incident.
"One person has died in hospital after the incident in central Stockholm. 15 injured adults and children are being treated at hospital. Nine of them have serious injuries," a statement on their website said.
Hospitals continue to be ready to take in more injured, the statement adds, but notes that it is too early to provide more detailed information.
"My thoughts go to all of those affected. We are full focused on the work needed to take care of injured and affected and are working together with different agencies," Stockholm County Council head doctor Johan Bratt said.
20:07: Stockholm public transport operator SL has been given the go ahead to start the metro again and the trains have gradually started to move, but will not be stopping at the central T-centralen station as well as Hötorget station, and a slow services is expected for the time being.
The commuter train has also been given permission to resume, but tracks may be backlogged with intercity trains.
"It could take a bit more time before we have fully working traffic again because it can take some time to get drivers in and get traffic flowing," SL press officer Henrik Palmér told news agency TT.
Buses will be redirected according to police cordons for the moment.
19:41 The Local's David Landes, like thousands of others, had a long trek home with public transportation on hold. But on Hornsgatan and Götgatan, busy streets on the trendy Södermalm island, the mood was calm. "It feels like a normal Friday - but with more people on the sidewalk, fewer cars on the roads- and no buses."
Photo: David Landes/TheLocal
19:30: Thousands of people are walking home this evening all across Stockholm after trains and buses were cancelled. Some underground trains have started running again, but delays are to be expected. Check travel advice here.
People walking home in central Stockholm. Photo: Tara Sonnorp/The Local
19:15: Police have brought two people in for questioning, but have not said who they are. "It absolutely does not mean that they are suspects," police spokesperson Lars Byström told the TT news agency.
19:08: The Local has been speaking to eyewitnesses and people near the scene today. "We saw people running and screaming. We were told to stay in the café at first. The place got emptied out quickly. There was such a big panic," a Spanish man told us.
18:41: Stockholm City Council has opened its doors to those who are not able to get home tonight because of trains and buses being cancelled. These premises are located at: Kammakargatan 30, Observatorielundens skola Norrtullsgatan, Hantverkargatan 3, Göta Ark Medborgarplatsen 25 and Bo Bergmans gata 4.
18:30: This picture has been published on Twitter of smoke rising from the building.
Watching the events unfold after a truck drove into Åhléns on Drottninggatan. pic.twitter.com/kxJLUOAsns— Emil Stenqvist (@svammel) April 7, 2017
18:15: A woman who works in an office block a hundred metres from the scene tells The Local they were not allowed to leave the building without being escorted by police. "There were police helicopters hovering over the square," she said. "I won't be able to get home because trains and buses are not running."
EYEWITNESSES: 'The wall came towards us like an avalanche'
18:05: The press conference has now concluded. The head of Sweden's security police, Anders Thorngren, said they had prepared for a similar incident. "Earlier this week we rehearsed a similar scenario. Säpo focuses on the intelligence work and who could behind this," he said.
While the identity of the attacker or attackers has not been confirmed, Säpo named terror attacks by lone wolves as one of the main threats to Sweden in its annual report published earlier this year.
18:00: Police have released CCTV images of a man they would like to trace "in connection with the suspected terror attack in Stockholm".
17:42: A police press conference has started in Stockholm. "A truck drove into Åhlens on Drottninggatan. We have truck and are in contact with the person who normally drives the truck," says Sweden's national police chief Dan Eliasson, adding that they do not have the individual or individuals driving the truck at the time of the attack.
17:23: A number of busy shopping locations in Stockholm have been evacuated at the request of the police. Along with the city's central railway station, the Åhlens department stores in the city centre, Odenplan, Fridhemsplan, Skanstull and Östermalmstorg have all been evacuated, as has the Mall of Scandinavia shopping centre in Solna. All of national film chain SF's Stockholm cinemas are closed this evening. Other events at Dramaten, Cirkus and Konserthuset have also been cancelled.
17:18: Images have been released of armed police at various locations in Stockholm.
Stockholm Central Station. Photo: Jessica Gow/TT
Police at Hamngatan in central Stockholm. Photo: Noella Johansson/TT
Police at Fridhemsplan. Photo: Maja Suslin/TT
17:05 The truck was rammed into a crowd just yards from the scene of a 2010 suicide bombing that left the perpetrator dead in the middle of the Christmas shopping rush.
16:57: Facebook users in Stockholm can mark themselves as safe from the incident by following this link.
16:50: Police have confirmed to The Local that people have been killed in today's incident.
"There are people injured and there have been fatalities, but exactly how many is not something we can say at the moment," a police spokesperson told The Local.
Police would not comment on reports that someone has been arrested for the attack.
16:38: Sweden's King Carl XVI Gustaf has released a statement about the incident.
"I and the entire royal family have sadly been informed about this afternoon's attack in Stockholm. The background to and extent of the incident is not yet know. We are following developments but our thoughts already go to those affected and their families," the statement reads.
16:33: The Local's contributor Miriam Bade took these pictures from near the scene of the crash.
16:31: Police have asked for Stockholm's central railway station to be emptied, a press spokesperson told news agency TT. Rail services to and from the station are currently suspended.
Photo: Anders Wiklund/TT
16:28: No one is currently being allowed to leave the Swedish parliament (Riksdag) building, which lies south of the area where the incident occurred on Drottninggatan. Few MPs are currently present in the building due to it being Friday afternoon.
16:22: A map showing the location of the Åhlens department store where the crash took place.
16:21: Stockholm police have advised the public to stay at home, avoid the city centre and "spread this to those you know".
Polisen uppmanar människor att stanna hemma och undvika city. Sprid detta till de ni känner. #stockholm— Polisen Stockholm (@polisen_sthlm) April 7, 2017
16:17: Trains to and from Stockholm's central railway station have been stopped at the request of the police, national railway operator SJ said, and all of the Stockholm metro is currently closed.
Det är stopp i tågtrafiken till och från Stockholm C på polisens begäran. Håll er uppdaterad via sj.se: https://t.co/U2Py2l8NbL— SJ AB (@SJ_AB) April 7, 2017
16:08: "Sweden has been attacked. Everything indicates an act of terror," PM Stefan Löfven said at a press conference on Friday afternoon.
"The government is informed and doing everything to help authorities with it."
Photos: Jessica Gow/TT
15:54: Swedish brewery company Spendrups, which owns the truck, said it had been hijacked earlier in the day.
"It's one of our distribution vehicles which runs deliveries. During a delivery to the restaurant Caliente someone jumped into the driver's cabin and drove off with the car, while the driver unloads," communication director Mårten Lyth told the TT news agency.
15:50 Video from above the scene.
Something's happening on Drottninggatan and around Stockholm. pic.twitter.com/YPbrZSe5Mb— Johnny Chadda (@johnnychadda) April 7, 2017
15:49: The police are advising the public to avoid Stockholm city centre near Sergels torg square.
15:41: The police have now confirmed that the vehicle was a truck and that there are reports of shots being fired, but that has not been confirmed.
"A lorry ran over people on Drottninggatan near Klarabergsgatan. There are reports of shots being fired but they have currently not been confirmed. It would have occurred in the proximity of Åhlens city (department store)," the Stockholm police website states.
"There are injured people but we have no further details on the extent of their injuries and the number of people injured."
15:35: At least three people are believed to have been killed, according to a Sveriges Radio reporter at the scene. A number of people were taken from the scene by ambulance according to TT.
15:33: An eyewitness at the scene told the TT news agency that medical staff were treating injured people on the street at the Drottninggatan/Kungsgatan intersection. "I also saw people with blankets over them," he said. "The whole body was covered."
People stood nearby filming until police came and ordered them to move away, the witness added.
15:26: The first images from the scene of the incident are starting to emerge.
Photo: Andreas Schyman/TT
15:20: "At 14:53 we got the call via SOS alarm that some people have injured other people on Drottninggatan near Klarabergsgatan. Now we're at the scene to deal with it," a police spokesperson has told The Local.
Police said they currently do not know how many people are injured and are working with emergency services to find out.
"I have no idea where the vehicle is now, this is the information available to me."
Police would not comment on whether the incident could be terror related, nor what has happened to the vehicle, and stated they are still assessing what has happened.
"I don't know where the vehicle is at the moment, but we will update that information on our website."
15:11: Police confirmed in a statement published at 2.53pm that they have received reports that "a person in a vehicle has injured other people".