At least three people are dead and a number of others injured after a vehicle crashed into a crowd in Stockholm on Friday afternoon, local time.
Several reports claimed shots were also fired at the scene.
Police have confirmed a large truck barreled into people walking on one of the city's major pedestrian streets. The truck then reportedly smashed into a department store.
According to local media, the vehicle belongs to a Swedish brewery. The company told reporters it had been hijacked earlier in the day.
Officials say they are treating the incident as terrorism-related.
Swedish Prime Minister Stefan Lofven told reporters, "The government is doing everything in its power to find out what has happened."
If it is confirmed to be a terrorist attack, it will be the first in Sweden since 2010, when a suicide bomber killed himself and injured two others in Stockholm.
Sweden's prime minister initially said one person had been detained in connection with the attack. But police later said no arrests had been made.