The explosion occurred near Central Square Tuesday afternoon, police said, urging people to avoid the area, ABC reports.

It is unclear what caused the explosion, which impacted a building that contains a Chase bank and apartments, authorities said.

Youngstown Fire Chief Barry Finley had initially characterized the incident as a natural gas explosion, but later said crews were working to determine if there was a gas leak.

"All I know for sure is that there was an explosion," Finley told reporters during a press briefing Tuesday evening.

Mercy Health said Tuesday evening it is treating seven people who were injured in the incident, including one person in critical condition.

Following a search of the building, a man and woman remain unaccounted for, Finley said. The man is an employee of the bank, the fire chief said. Police were searching for his vehicle in the wake of the explosion, he said.

"Until then, we have to assume he is in the building," Finley said.

The floor collapsed into the basement, which was flooded, and search crews were working to send a mini-drone in there to aid in the search effort, Finley said.