The man was shot on the Roskildegatan street north of Pildammsparken in the early hours of Wednesday. According to Malmö police he was a janitor who was there to spread salt on icy walkways.
"He was there to shovel snow and then he gets shot," one of the man's colleagues told regional newspaper Sydsvenskan, which reports he is in his fifties.
The man is not previously known to police. "What happened on the scene we don't really know at the moment," Malmö police chief Stefan Sintéus told the TT news agency.
Police seized several suspects, understood to be linked to gang violence, for questioning.
"They are younger people who are extremely criminally active. We don't want to state their age and number for the time being," said Sintéus. "They are suspected of this incident, among other things."
Later in the day they confirmed that one of them, a 15-year-old boy, had been arrested on suspicion of attempted murder.
Police were called to the scene just before 2am on Wednesday after residents in the area heard gunshots. The victim was found injured and was taken to hospital with life-threatening injuries.
At around 3.30pm a hospital press officer told The Local his condition was still life-threatening.
The man was found injured in central Malmö. Photo: Johan Nilsson/TT
The new shooting is the latest in a spate of recent violence in Malmö, where two murders in particular have left investigators perplexed: the fatal shootings of a 24-year-old dentist in December and a 16-year-old student in Rosengård last month.
In both cases, there is nothing to suggest the victims were involved in any criminal activity and they had no known enemies.