An Australian tourist has described witnessing a stolen truck ploughing through a crowd into a department store in central Stockholm, killing four people and wounding 15, in what appears to be a terror attack.
"I turned around and saw a big truck coming towards me. It swerved from side to side. It didn't look out of control, it was trying to hit people," Glen Foran, an Australian tourist in his 40s, told Reuters after Friday's attack.
"It hit people, it was terrible. It hit a pram with a kid in it, demolished it," he said.
"It took a long time for police to get here. I suppose from their view it was quick, but it felt like forever."
Swedish police said they had arrested one person after earlier circulating a picture of a man wearing a grey hoodie.
They did not rule out the possibility other attackers were involved.
"Sweden has been attacked. Everything points to the fact that this is a terrorist attack," Prime Minister Stefan Lofven told reporters.
There was no immediate claim of responsibility.
Part of central Stockholm was cordoned off and the area was evacuated, including the main train station. All subway traffic was halted on police orders. Government offices were closed.
Many police and emergency services personnel were at the scene, said a Reuters witness who saw policemen put what appeared to be two bodies into body bags. Bloody tyre tracks on Drottninggatan (Queen Street) showed where the truck had passed.
The truck had been stolen while making a beer delivery to a tapas bar further up Drottninggatan, Spendrups Brewery spokesman Marten Lyth said. A masked person jumped into the cab, started the truck and drove away.
"We were standing by the traffic lights at Drottninggatan and then we heard some screaming and saw a truck coming," a witness who declined to be named told Reuters.
Police said four people had died and 15 were injured. National news agency TT said those hurt included the delivery driver, who had tried to stop the hijack.
Several attacks in which trucks or cars have driven into crowds have taken place in Europe in the past year.
Stockholmers opened up their homes and offered lifts to people who were unable to get home or needed a place to stay.
Sweden has not been hit by a large-scale attack, although in December 2010, a man blew himself up only a few hundred yards from the site of the latest incident in a failed suicide attack.
In February US President Donald Trump falsely suggested there had been an immigration-related security incident in Sweden, to the bafflement of Swedes.
Swedish authorities raised the national security threat level to four on a scale of five in October 2010 but lowered the level to three, indicating a "raised threat", in March 2016.
Neutral Sweden has not fought a war in more than 200 years, but its military has taken part in UN peacekeeping missions in a number of conflict zones in recent years, including Iraq, Mali and Afghanistan.