Swedish police say at least three killed and many injured in the incident on Drottninggatan street in
Swedish police officers guard the area after the truck crashed into the department store.
Several attacks in which trucks or cars have driven into crowds have taken place in Europe in the past year.
In London last month, a man in a car ploughed into pedestrians on Westminster Bridge, killing four, and then stabbed a policeman to death before being shot by police.
In Nice, France, last July, a truck killed 86 people celebrating Bastille Day, and one in Berlin in December smashed through a Christmas market, killing 12 people.