Police officers in special equipment walk through a Jehovah’s Witness building on Thursday in Hamburg, Germany, Thursday. Jonas Walzberg/dpa via AP

BERLIN — Shots were fired inside a building used by Jehovah’s Witnesses in the northern German city of Hamburg on Thursday evening, with several people killed and wounded, police said.

“We only know that several people died here; several people are wounded, they were taken to hospitals,” police spokesperson Holger Vehren said of the shooting in the Gross Borstel district of Germany’s second-biggest city.

He said he had no information on the severity of the injuries suffered by the wounded. Police did not confirm German media reports, which named no sources, of six or seven dead.

In a Twitter update in the early hours Friday, Hamburg police said they believed there was only one shooter and they were gradually rolling back security forces from the area.

“The investigation into the motive behind the crime continues,” police said.

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 p.m. 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.

Student Laura Bauch, who lives nearby, said “there were about four periods of shooting,” German news agency dpa reported. “There were always several shots in these periods, roughly at intervals of 20 seconds to a minute,” she said.

She said she looked out her window and saw a person running from the ground floor to the second floor of the Jehovah’s Witnesses hall.

Gregor Miesbach, who lives within sight of the building, was alerted by the sound of shots and filmed a figure entering the building through a window. Shots can then be heard from inside. The figure later apparently emerges from the hall, is seen in the courtyard and then fires more shots inside.

Miesbach told German television news agency NonstopNews that he heard at least 25 shots. After police arrived, one last shot followed about five minutes later, he said.

Police had no information on the event that was underway 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 which 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.