"One person has been arrested and five have been taken in for questioning in connection with the shooting," said police control room officer Hans Nilsson.
None of those hurt in the attack received life-threatening injuries, and police said they did not believe the attack was terror-related.
Emergency services received several calls reporting the shooting at around 10.30pm on Thursday after several men were hurt in the central part of the town.
Eight ambulances were sent to the scene and four men were taken to hospital, of whom two had gunshot injuries and one who had been injured by a knife. The men were between the ages of 18 and 25.
"According to the doctors at the hospital, the injuries are serious but not life-threatening," said Nilsson.
"The five people who have been questioned have been released, and the man who has been arrested is suspected of attempted murder," he said, adding that he could not rule out the possibility of further people being arrested in connection with the shooting.
He said that some of those involved were known to police.
The area where the shooting took place was closed off overnight while police technicians and dogs worked at the scene. Police have opened an investigation into attempted murder but could not say what the motive behind the shooting was.
Trelleborg is a town home to almost 30,000 inhabitants in the far south of Sweden.
"Trelleborg is a calm town and it's a small town, so this kind of thing is not normal in Trelleborg," said Fredrik Bratt, a police spokesperson for the southern region.