A truck slammed into a crowd of people outside a busy department store in central Stockholm on Friday, causing "deaths" in what the prime minister described as an "terror attack."
"There are deaths, and many injured," Nina Odermalm Schei, a spokeswoman for Swedish intelligence agency Sapo, told AFP, without giving a precise figure.
"Sweden has been attacked. Everything points to a terror attack," said Prime Minister Stefan Lofven.
Pictures showed a large blue truck with a mangled undercarriage smashed into the Ahlens department store.
A spokeswoman for transport company Spendrups told AFP that the truck "had been stolen during a delivery to a restaurant."
Witnesses described scenes of terror and panic.
One witness identified only as Dimitris told the Aftonbladet daily that the truck came "out of nowhere."
"I couldn't see if anyone was driving but it was out of control. I saw at least two people get run down. I ran as fast as I could away from there," he said.
Another shopper, 66-year-old Leander Nordling, was at Ahlens when he suddenly heard a loud bang.
"It sounded like a bomb exploding and smoke starting pouring in through the main entrance," he told daily Aftonbladet.
He and fellow shoppers took refuge in a supply closet inside the department store.
"After that the building was evacuated ... There were a lot of guards who took care of us outside and they urged us to leave the scene immediately," Nordling said.
- 'Attack on us all' -
The incident occurred just before 1300 GMT at the corner of the store and Drottninggatan, the city's biggest pedestrian street, above ground from Stockholm's central subway station.
Thick smoke was rising from the scene, while video images showed an area blocked off by police and crowds gathering around the police cordon.
Police vans circulating in the city using loudspeakers urged people to go straight home and avoid large crowds.
The centre of the usually buzzing city was in lockdown, with the central train station evacuated and other shops quickly emptied of shoppers.
The Stockholm metro was completely shut down, with the attack taking place at the city's T-Centralen station, through which all the city's lines pass.
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.
European politicians reacted with solidarity to the news of the attack, with European Commission President Jean-Claude Juncker saying that it was an "attack on us all."
A spokesman for German Chancellor Angela Merkel said: "Our thoughts go out to the people in Stockholm, to the injured, their relatives, rescuers and police.
"We stand together against terror."
- Trucks as weapons -
The attack followed a string of assaults in Europe by people using vehicles as weapons.
The deadliest attack came last year in France on the Bastille Day national holiday of July 14, when 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 later 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.
And in December, a man hijacked a truck and slammed into shoppers at a Christmas market in Berlin, killing 12 people.
That attacker was shot dead by police in Milan four days later, and the rampage was claimed by the IS.
In 2014, IS called for attacks on citizens of Western countries and gave instructions on how they could be carried out without military equipment, using rocks or knives, or by running people over in vehicles.
Attacks have not been limited to Europe.
In 2014, a Muslim convert used his car to mow down two soldiers near Montreal, killing one of them. The attacker was shot dead by police as he climbed out of his wrecked vehicle brandishing a knife.
There have also been false alerts, however.
Earlier Friday, Belgium dropped terrorism charges against a driver who sped into a crowded shopping area in Antwerp last month, which sparked fears of a copycat terror attack.
However, the driver, a Tunisian man, remains in custody on a weapons offence related to the incident, the federal prosecutor's office said.