"Police received a call from SOS Alarm that a person in a vehicle has injured other people on Drottninggatan," police wrote on Twitter.
The incident occurred just before 1300GMT at the corner of the Ahlens department store and Drottninggatan, the city's biggest pedestrian street, above-ground from Stockholm's central subway station.[caption id="attachment_56991" align="alignright" width="300"] Witnesses said crowds ran for their lives in central Stockholm TWITTER[/caption]
Thick smoke was rising from the scene, while video images showed an area blocked off by police and crowds gathering around the police cordon.
Helicopters could be heard hovering in the sky over central Stockholm, and a large number of police cars and ambulances were dispatched to the scene, witnesses said.
While it was unclear whether the incident was an attack or an accident, it follows after a series of attacks in Europe by people using vehicles as weapons.
Swedish Prime Minister Stefan Lofven has told a press conference that one person has been arrested.
Lofven said the country had been attacked and that everything indicated that the truck driven into a crowd in central Stockholm on Friday was an act of terrorism, news agency TT reported.
Swedish police said three people were confirmed dead, the news agency reported.
The worst attack was last year in France on the Bastille Day national holiday of July 14, in which a man rammed a truck into a crowd in the Mediterranean resort of Nice, killing 86 people.
He was shot dead by police, and the Islamic State group claimed responsibility.
Last month, Khalid Masood, a 52-year-old convert to Islam known to British security services, drove a car at high speed into pedestrians on London's Westminster Bridge before launching a frenzied knife attack on a policeman guarding the parliament building.
The incident killed five people, while Masood himself was shot dead by police.
VIDEO: People running after truck reportedly drives into crowd on Stockholm street https://t.co/fQZpiKm7Yr pic.twitter.com/kZgbO2kjhP — RT (@RT_com) April 7, 2017