A hijacked beer truck plowed into pedestrians at a central Stockholm department store on Friday, killing four people, wounding 15 others and sending screaming shoppers fleeing in panic in what Sweden's prime minister called a terrorist attack.

A nationwide manhunt was launched and one person was arrested following the latest use of a vehicle as a weapon in Europe.

Nearby buildings were locked down for hours in the heart of the capital — including the country's parliament — and the main train station and several large malls were evacuated.

"Sweden has been attacked," Prime Minister Stefan Lofven said in a nationally televised news conference. "This indicates that it is an act of terror."

Sweden's Prime Minister Stefan Lofven places flowers near where a hijacked beer truck plowed into pedestrians at a department store in Stockholm, Sweden, on Friday. (Fredrik Sandberg/TT News Agency/Reuters)

Later Friday night, Lofven laid a bouquet of red roses and lit a candle near the site of the attack.

"The country is in a state of shock," he said. "The aim of terrorism is to undermine democracy. But such a goal will never be achieved in Sweden."

There was no immediate claim of responsibility for the attack. Police arrested a man in Marsta, a northern Stockholm suburb close to the city's international airport, as a possible suspect.

CBC News speaks with Annevi Petersson, who witnessed Friday's crash in central Stockholm 2:50

The stolen beer truck travelled for more than 500 metres along a main pedestrian street known as the Drottninggatan before it smashed into a crowd outside the upscale Ahlens department store about 3 p.m. It came to rest in the entrance to the building. TV footage showed smoke coming out of the store after the crash.

"People were screaming and running in all directions," said Brandon Sekitto, who was in his car nearby. "(The truck) drove straight into the Ahlens entrance."

"I saw the driver, a man in black who was light around the face," Brandon told Swedish daily Dagens Nyheter. "Some women were screaming, 'Run! Run!"'

Late into the night, forensic experts suits could be seen working on the truck, collecting evidence.

Central Stockholm evacuated

Although there was initial confusion on the number of victims, police told reporters in the evening that four people had been killed and 15 were wounded, nine of them seriously.

Authorities evacuated the city's nearby Central Station, a hub for regional trains and the subway system. All trains to and from the main station were halted and several large shopping malls in Stockholm were shut down.

On the highway outside of Stockholm, traffic was jammed with people trying to make it into the city, CBC's Julian Sher reported from Uppsala, an hour north of the capital.

Jan Evensson of the Stockholm police told a news conference that the man who was arrested looked like the person depicted wearing a greenish hood in a surveillance camera photo that police released earlier. He said police were "particularly interested" in him.

Police released these photos of the suspect on Friday. 'We still cannot rule out that more people are involved,' Dan Eliasson, head of Sweden's national police, told reporters on Saturday. (Police/TT via AP)

"We continue to investigate at full force," Evensson said, urging people not to go to central Stockholm on Friday night.

Stefan Hector of Sweden's national police said the working hypothesis was that "this is an act of terror."

The Swedish brewery Spendrups said one of its trucks had been hijacked just a few blocks from the crash scene earlier Friday.

"Someone jumped into the truck and drove it away while the driver was unloading his delivery," Spendrups spokesman Marten Luth told the Swedish news agency TT. The truck driver was not injured, he said.

Condolences from around the world

Friday's truck crash was near the site of a December 2010 attack in Stockholm in which Taimour Abdulwahab, a Swedish citizen who lived in Britain, detonated a suicide bomb, killing himself and injuring two others.

Swedish King Carl XVI Gustaf cut short a visit to Brazil on Friday to return home and sent the royal family's condolences to the families of the truck attack victims.

Condolences poured into Sweden. In neighbouring Finland, President Sauli Niinisto said he was shocked by the "maniac act of terror," adding "every terror attack is to be equally condemned. But it touches us deeply when such an attack takes place in our Nordic neighborhood."

Danish Prime Minister Lars Loekke Rasmussen called the attack a cowardly attempt "to subdue us and the peaceful way we live in Scandinavia."The mayor of London, where five people were killed in a vehicle and knife attack last month, said the British capital "stands united with Stockholm."

Sadiq Khan said it appears Sweden has "seen a despicable act of terrorism aimed at harming innocent people and attacking our shared values of democracy, freedom, justice and tolerance."

He says Londoners know what it is to suffer from terrorism, and "we share a steely determination with the people of Stockholm that we will never allow terrorists to succeed."

Canadian Prime Minister Justin Trudeau condemned the attack and said Canada stands in solidarity with Sweden.

"Canada grieves with our Swedish friends in this difficult time and we offer all possible assistance," he said in a statement.

We offer our deepest condolences to the families & friends of those killed in today’s cowardly attack in Stockholm: <a href="https://t.co/g4AlLJGCjb">https://t.co/g4AlLJGCjb</a> —@JustinTrudeau

German Chancellor Angela Merkel's spokesperson said the German government's "thoughts are with the people in Stockholm, the injured, the relatives, first responders and police."

Steffen Seibert said Friday on Twitter following the apparent attack in Sweden: "We stand together against terror."

Germany experienced a truck attack on a busy Berlin Christmas market in December, in which 12 people were killed.