YOUNGSTOWN, Ohio (AP) — A massive explosion blew out much of the ground floor of an apartment building, killing a bank employee and injuring several other people. Police and emergency officials initially blamed natural gas, but the fire chief later said the cause is under investigation.

The blast happened around 2:45 p.m. Tuesday, collapsing part of the ground floor of Realty Tower into its basement and sending the façade across a street where both sides had been blocked off by orange construction fencing. The 13-story building has a Chase Bank branch at street level and apartments in upper floors.

Speaking at a news conference Wednesday, city officials said the state fire marshal's office was leading the investigation into the cause, and it wasn't known when a determination may be made.

The bank employee, 27-year-old Akil Drake, had been seen inside the building right before the blast, the Youngstown Police Department said Wednesday. Youngstown Fire Chief Barry Finley said in a news conference Tuesday that firefighters rescued several people and cleared the building to ensure no one else was hurt.

Finley said Wednesday that two people — Drake and a woman whose name has not been released — were initially unaccounted for after the blast, so firefighters and other emergency responders remained on scene for several hours to locate them. Finley said the woman was found in a hospital where, for unknown reasons, she had been registered under another name.

Drake's body was eventually found in a basement.

“We were not going to leave there until we found him. His family deserved closure,” Finley said.

JPMorgan Chase mourned his loss and said it would work with local officials. “Our hearts go out to their family as well as our injured employees, their families and others affected by this tragedy," a company statement read.

Police and the Mahoning County Emergency Management Agency said there was a natural gas explosion, but the fire chief later said it was too early to say.

"We have no idea what caused the explosion. We know that there was an explosion and it did a lot of damage to the bottom of the building,” Finley said Tuesday. He said none of the apartments in the building are habitable.

Seven injured people were taken to Mercy Health Hospital in Youngstown. Finley said one woman remained in critical condition Wednesday.

The blast shook downtown Youngstown, a city of about 60,000 residents. Bricks, glass and other debris littered the sidewalk.