A six-story apartment complex partially collapsed Sunday evening in the city of Davenport, Iowa, authorities said. It was not immediately clear if there were any fatalities or how many people may be missing or trapped in the building.

Davenport Mayor Mike Matsen said there were “several people unaccounted for,” but did not give a specific number or range. 

The collapse happened shortly before 5 p.m. local time, Davenport fire chief Mike Carlsten said. The cause of the collapse was not immediately clear.

Seven people were rescued by fire crews and more than a dozen others were escorted out of the building as they were “self evacuating,” Carlsten said. 

Specialized rescue teams have been called in to assist with the search of the debris. Crews would continue searching throughout the night, Carlsten said.

Fire crews arriving on scene also found a “large natural gas leak,” Carlsten said. It was not clear if the leak happened as a result of the collapse or if gas had been leaking prior to the incident.

The fire department was also concerned about the structural stability of the rest of the building. 

“Even while we were on scene, we still had multiple secondary drops of debris coming from that structure,” Carlsten said. “We want to make sure all our responders can are able to process through in a safe manner, but we still want to get through there as quickly as possible.”

The owner of the building had secured permits for repairs on the exterior brick walls of the building, officials said. The owners had two other permits issued for exterior brickwork over the last year, officials said. Falling bricks that were reported over the last week were part of that repair work.

Various tenants in the building have previously called the city to complain about different aspects of the building. “Notices and orders were issued to the building owner for repairs,” one official said.

Davenport is located about 70 miles from Cedar Rapids along the eastern part of the state’s border with Illinois.