Police arrest a man in Stockholm terror attack that killed 4

• At least four people are dead and several injured after a truck rammed into a crowd on a main shopping street in central Stockholm.
• Sweden's prime minister has said the evidence points to a terrorist attack.
• The police released the picture of a man sought in connection with the apparent attack.
• The central train station in the city is being evacuated by the police.

At least four people died and 15 more were injured after a truck drove into a crowd in Stockholm on Friday afternoon, the police said in a press conference, the Swedish police said in a press conference. By 8 p.m. local time, a man was arrested in connection with the crime 25 miles from the Swedish capital.

Swedish Prime Minister Stefan Lofven said it was believed to be "a terror attack," according to the Associated Press.

One person was arrested in connection with the attack Friday evening, Swedish police said, according to the AP.  Local newspaper Aftonbladet has reported that a man with minor injuries has confessed to being behind the wheel of a hijacked truck. He was detained in Märsta, a suburb 25 miles north of Stockholm.

Earlier, the police said were reportedly looking to speak with a man who was wearing a green jacket, white shoes, and a gray hoodie.

The police released a picture that was taken near the scene of the carnage Friday and urged people to call the police if they spotted the man. They have not confirmed whether the man in the circulated picture was the same one that was arresed. By 8 p.m. local time, two people not identified as suspects have also been taken in for questioning, Aftonbladet reports.

"We do not know if this is an isolated incident or if we can expect anything more," the police said at a press conference.

In a statement, the police also said they could not rule out terrorism based on other recent events in Europe.

At about 3 p.m. local time, the truck drove into people on a busy street in central Stockholm and crashed into a department store. Aftonbladet is reporting that the Swedish beermaker Spendrups said one of its trucks had been hijacked earlier Friday.

The police evacuated the city's main train station, where an operation is ongoing. Reports of shooting taking place in another part of town have surfaced, but the police have not confirmed those reports.

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The entire subway system in the city has been shut down, and the police have cut off the area around where the truck crashed into the department store, Åhlens City. According to local newspaper Expressen, all Stockholm hospitals have gone into emergency mode.

A local reporter, Martin Svenningsen, who was present at the scene, told the Swedish radio station SR Echo that he "saw at least three dead, but there are probably more," adding: "It's a complete mess here."

Facebook's Safety Check feature has been activated for the incident in Stockholm, and the police are telling people to avoid the city centre.

Many witnesses are telling local media outlets that they saw the truck drive into people on Queen Street and then into a store's display window. They report "total confusion" and "complete chaos" in the city. A witness said an alarm went off in the department store and everyone was asked to leave the building.

The police warned people in central Stockholm of a "terror attack," according to witnesses who spoke with Aftonbladet.

Police officers is some major cities in Norway have been allowed to carry weapons following the apparent attack in Stockholm, and the Helsinki police said they would tighten security measures in the center of the Finnish capital.

This is a developing story.