About 30 people are reported injured in the incident, which occurred near the Kiepenkerl statue in the old town. Some are said to be in a serious condition.
Police have asked people to avoid the city centre.
There is a restaurant located in the vicinity of the Kiepenkerl statue and photographs posted on social media showed tables and chairs strewn at the scene.
Ulrike Demmer, the federal government’s deputy spokesperson, said the government’s thoughts were with the victims and their families.
In December 2016, a lorry ploughed into a crowd at at Christmas market in the German capital, Berlin, killing 12 people.