The incident was in Drottninggatan, a street in a busy shopping district in the centre of the Swedish capital.
Police said a number of people had been hurt in the incident, which comes after trucks were used in terror attacks in Nice and Berlin last year.
Newspaper Aftonbladet quoted a witness saying they saw hundreds of people running for their lives near the Ahlens mall
Another witness told the newspaper that the out-of-control truck ran over at least two people.
Pictures on social media showed the lorry had crashed into the corner of Mall with its cab on fire.
An Aftonbladet reporter on the scene said police suspected the crash was terror related.
More to follow