Breaking: Swedish Prime Minister Stefan Lofven says everything indicates this is "a terror attack"
All subway traffic in the city has been shut down, according to Swedish news agency TT
Breaking: Swedish security services tell Sky News there are "plenty of casualties", no confirmation of any gunfire at this stage.
Police say they have received information regarding possible shots being fired, but stress this has not been confirmed.
They are telling people to avoid the city centre.
Broadcaster SVT is reporting at least five people have been killed, but again, this has not been confirmed by police.