Local media said the man arrested had claimed responsibility for the attack. At least four people died when the truck was driven into a department store in central Stockholm.
Swedish police have arrested a man in north Stockholm early Friday evening in connection with the truck attack which killed at least four people and injuring 15 others earlier in the day.
The man had confessed to driving a truck into a department store in the centre of the city, Swedish daily newspaper Aftonbladet reported.
The centre of Stockholm remains on lockdown after a Spendrups beer truck, which had been carjacked earlier, crashed into an upscale department store.
Swedish Prime Minister Stefan Lofven called the truck attack "an act of terrorism."
Swedish police also released a photo of a man who is wanted for questioning.
Police said they were also questioning two other people, but they are not suspected of any crime currently.
Witness Jan Granroth said, "we stood inside a shoe store and heard something ... and then people started to scream. I looked out of the store and saw a big truck."
TRT World's Oliver Whitfield-Miocic reports.
Shots were fired after the crash and Swedish television showed smoke coming out of the department store, and people were seen fleeing the scene.
Police are warning people to avoid central Stockholm around the downtown Sergels Torg square.
Public transport services including the subway has also been shutdown in the area.
Sweden's national rail company SJ said all trains to and from Stockholm's central station would be cancelled for the rest of the day.
The most recent such attack in Stockholm was on December 11, 2010, when an Iraqi-born Swede, Taimour Abdulwahab al-Abdaly, detonated two devices, including one that killed him, in central Stockholm.
Germany were the first country to sympathise with Sweden after the attack.
Chancellor Angela Merkel's spokesman said, "Our thoughts go out to the people in Stockholm, to the injured, their relatives, rescuers and police. We stand together against terror."
"An attack on any of our member states is an attack on us all," European Commission President Jean-Claude Juncker said in a message of condolences to the victims, adding the aim appeared to strike at "our very way of life."
Finnish President Sauli Niinisto said he is shocked by the "maniac act of terror" in Stockholm.
"Every terror attack is to be equally condemned. But it touches us deeply when such an attack takes place in our Nordic neighbourhood."
"France expresses its sympathy and solidarity with the families of the victims and all Swedes," French President Francois Hollande tweeted in French.
Other world leaders have also taken to social media site Twitter to share their support wth Sweden.
My heart is in #Stockholm this afternoon. My thoughts are with the victims and their families and friends of today's terrible attack.— Donald Tusk (@eucopresident) April 7, 2017
Deeply sad to hear about #Stockholm, condemn terror attack. Condolences to our Swedish friends, we will stand firm & together #dkpol— Anders Samuelsen (@anderssamuelsen) April 7, 2017
India stands firmly with the people of Sweden in this hour of grief. @SwedishPM— Narendra Modi (@narendramodi) April 7, 2017
Deeply concerned by shocking incident in #Stockholm. Britains thoughts are with the victims, their families and the whole of #Sweden— Boris Johnson (@BorisJohnson) April 7, 2017