Witnesses described a chaotic scene in the moments after a truck rammed into a busy Stockholm department store in what Prime Minister Stefan Lofven described as a "terror attack."

Swedish brewery Spendrups said its truck, which appeared to have been used in the attack, was stolen on its way to a restaurant delivery earlier in the day. Photos from the scene showed the beer truck sticking out of the Ahlens department store.

"There is total confusion. I do not know how many are injured - many people are totally shocked," one witness, Leif Arnmar, who was working in the department store, told SVT.

Police confirmed at least three people were killed in the attack and eight others were injured. Despite initial reports that one person was arrested shortly after the attack, police said late Friday that no suspect was in custody.

It's the most significant attack in Sweden since December 2010, when an Iraqi-born Swede, Taimour Abdulwahab al-Abdaly, detonated two devices, including one that killed him, in central Sweden.

On social media, witnesses, some working in nearby office buildings at the time, immediately sensed something was wrong.

Some onlookers posted video on Twitter of people sprinting away from the scene followed by heavily armored police arriving to secure the area.

Witness Jan Granroth told Swedish newspaper Aftonbladet, that “we stood inside a shoe store and heard something … and then people started to scream.” He says: “I looked out of the store and saw a big truck.”

The capital was locked down soon after the attack as police set up barricades, suspended public transport and warned people to avoid the city center.

Police also evacuated the central train station close to where the attack took place.

Contributing: Associated Press