“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.

David Semonian, a US-based spokesman for Jehovah’s Witnesses, told The Associated Press in an emailed statement early Friday that members “worldwide grieve for the victims of this traumatic event.”

“The congregation elders in the local area are providing pastoral care for those affected by the event,” he wrote. “We understand that the authorities are still investigating the details of this crime. We appreciate the courageous help provided by the police and emergency services.”

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.

Hamburg security officials said there would be a news conference Friday afternoon to discuss details.

The scene of the shooting was the Jehovah’s Witnesses’ Kingdom Hall, a modern and boxy three-story building next 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.

Through the night, forensic investigators in protective white suits could be seen walking through the building continuing their work.

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.

His video, posted online by Bild newspaper, showed a person firing multiple shots into the building through a first-floor window before the lights inside the room went out.

Early Friday morning, investigators could be seen working outside the building as a light snow fell, placing yellow cones on the ground and windowsills to mark evidence.

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 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.