The shooting took place in the Gross Borstel district, a few kilometers north of the downtown area of Germany's second-biggest city."We only know that several people died here; several people are wounded, they were taken to hospitals," police spokesman Holger Vehren said.

He said he had no information on the severity of the injuries suffered by the wounded.

The scene of the shooting was the Jehovah's Witnesses' Kingdom Hall, a modern and boxy three-story building next door to an auto repair shop.

Vehren said police were alerted to the shooting about 9.15 pm local time and were on the scene quickly.

He said that after officers arrived and found people with apparent gunshot wounds on the ground floor, they heard a shot from an upper floor and found a fatally wounded person upstairs who may have been a shooter. He said police did not have to use their firearms.

Vehren said there was no indication that a shooter was on the run and that it appeared likely that the perpetrator was either in the building or among the dead.

Two witnesses interviewed on n-tv television, whose names weren't given, said they heard 12 shots.

Police had no information on the event that was under way in the building when the shooting took place.

They also had no immediate information on a possible motive. Vehren said that "the background is still completely unclear."

Hamburg Mayor Peter Tschentscher tweeted that the news was "shocking" and offered his sympathy to the victims' relatives.

Jehovah's Witnesses are part of an international church, founded in the United States in the 19th century and headquartered in Warwick, New York. It claims a worldwide membership of about 8.7 million, with about 170,000 in Germany.

Members are known for their evangelistic efforts that include knocking on doors and distributing literature in public squares. The denomination's distinctive practices include a refusal to bear arms, receive blood transfusions, salute a national flag or participate in secular government.