Swedish police have arrested a man in north Stockholm and he has confessed to carrying out a deadly truck attack in the centre of the city which killed at least four people, daily Aftonbladet reports.
Another 15 were wounded, nine of them seriously, in the horror attack after a hijacked truck rammed into a crowd then crashed into a department store in central Stockholm, Sweden.
Images from the scene show people running for their lives outside the up-market Ahlens department store on Drottninggatan, which is the biggest pedestrian street in the Swedish capital and above the city's central subway station.
Swedish Prime Minister Stefan Lofven says everything indicates this is a "terror attack", Associated Press reports.
"Sweden has been attacked," he said. "This indicates that it is an act of terror."
The arrested man has some light injuries and said he was responsible for the attack, Aftonbladet said citing several unnamed sources on Friday.
Police declined to comment.
Earlier Swedish police said they were interviewing two people in relation to a deadly truck attack in the capital Stockholm.
"I can confirm that we have taken in two people for questioning, but that does not necessary means that they are suspects," police spokesman Lars Bystrom said on Friday.
"We want to talk to everybody who knows anything about this and sometimes it's better to talk at the police station than place of event."
Swedish police earlier circulated a picture of a person they say is of interest.
Mats Lofving, head of Swedish police's National Operations Department (NOA) said the picture, which appeared to be CCTV footage, was taken close to the time of the incident on Friday, in the vicinity of the incident.
"I have a picture of a person who has been seen at the location at this point in time. We want to get in contact with this person," he told a news conference.
The grainy image shown by police showed a man wearing a jacket with a dark hood over a bright T-shirt and dark trousers.
Stockholm County Council said that four people were killed in the attack; 15 wounded, nine of them seriously after a hijacked truck rammed into a crowd then crashed into a department store in central Stockholm, Sweden.
Officers were seen pinning a man down after the incident.
Three armed men jumped out of the truck during the incident, according to Swedish media outlet Expressen.
A witness inside a car, who declined to be named, heard screaming as the truck approached.
"Then it drove into a pillar at Ahlens City (department store) where the hood started burning. When it stopped we saw a man lying under the tire. It was terrible to see," the man told Reuters.
Other witnesses told Aftonbladet of hundreds of shoppers ran away in panic.
"We stood inside a shoe store and heard something ... and then people started to scream," witness Jan Granroth said.
"I looked out of the store and saw a big truck."
Another witness named Anna said she "saw hundreds of people run, they ran for their lives".
"I turned and ran as well," she said.
A man named Dimitris said two people were run over in the chaos.
"I went to the main street when a big truck came out of nowhere," he said.
"I could not see if anyone was driving it but it got out of control. I saw at least two being run over.
"I ran as fast as I could."
The usually busy pedestrian mall has been locked down by police and citizens have been urged to avoid the area.
Stockholm locals have posted confronting images and videos on social media, some that show streets smeared with blood and strewn with covered bodies covered.
Emergency services were filmed spraying foam on the truck.
Swedish broadcaster SVT said shots were fired at the scene and the Swedish news agency TT said several people were rushed away in ambulances.
Thick smoke could be seen on the streets, while video showed an area blocked off by police and crowds gathering around the police cordon, according to AFP.
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 Islamic State has not claimed responsibility for the crash, it has the hallmarks of other attacks carried out by the terror organisation's supporters.
In London six people, including the attacker died, after Khalid Masood drove a car onto Westminster Bridge hitting pedestrians in late March.
A similar incident occurred in Nice, France, last July killing 86 people, while another truck attack killed 12 at a Christmas market in Berlin in December.
In a statement, Swedish police said they could not exclude that the Stockholm incident was an act of terror based on other events in Europe.