A gunman believed to have been acting alone has killed several people in a Jehovah’s Witness building in the German city of Hamburg, police have said.

Shots were fired at the Jehovah’s Witnesses’ Kingdom Hall in the Gross Borstel district, with police alerted at around 9.15pm on Thursday.

Police have not confirmed how many people were killed or injured, describing the number as “several”.

One witness told reporters: “We heard shots.

“There were 12 continuous shots.

“Then we saw how people were taken away in black bags.”

Police spokesperson Holger Vehren said officers heard a shot from an upper floor of the building after they arrived and found a person upstairs who may have been a gunman.

Mr Vehren said: “We only know that several people died here; several people are wounded, they were taken to hospitals.”

He said police did not have to use their firearms.

In a statement posted on Twitter, Hamburg Police said: “We found a lifeless person in a community centre in #GroßBorstel who we believe could be a perpetrator.

“In order to rule out the involvement of other perpetrators, we carry out checks and search extensively.”

The motive for the attack is currently unclear.

Hamburg Mayor Peter Tschentscher said: “I extend my deepest sympathy to the families of the victims.

“The forces are working at full speed to pursue the perpetrators and clarify the background.”

Police added that a large operation was under way in the next-door Alsterdorf district, in the northern part of the city. The area is a few kilometres north of the downtown area of Hamburg, which is Germany’s second-biggest city.

A number of armed officers were pictured near the scene alongside dozens of police cars.