"There are several people who have experienced confirmed gunshot wounds", a statement issued by Police Skåne read.
Swedish police said four people were rushed to hospital but the seriousness of their conditions is not yet known.
A police spokesman said: "We have received several reports of a shooting in Trelleborg".
"I do not have any more information at this time".
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Police have launched a major operation.
Trelleborg has been placed on lockdown by armed cops with reports that at least four people suffered gunshot wounds. But we are at the scene and investigating'.
One witness told The Express: "There were many shots. We saw someone running outside", an eyewitness told the Swedish publication Expressen.
Another said: "I was at home at my computer when I heard a loud bang".
Forensics officers and police dogs have arrived on the scene. Residents have been advised by law enforcement to avoid the central part of the town.