One firefighter was killed — and at least nine other firefighters and two civilians injured — in a large home explosion in Northern Virginia’s Loudoun County Friday night, officials said.

In a news briefing late Friday night, Loudoun County Fire and Rescue Assistant Chief of Operations James Williams said that fire crews were first called to the home in the community of Sterling at about 7:40 p.m. local time.

Soon after firefighters arrived, an explosion occurred, Williams said.

One firefighter was killed in the explosion, Williams disclosed. The victim was not immediately identified. Nine other firefighters and two civilians were rushed to area hospitals with unknown injuries.

“The nine firefighters have some serious injuries, as well as some less severe injuries,” Williams said.

Aerial footage from CBS affiliate WUSA-TV showed widespread debris from the explosion, with heavy flames burning and smoke billowing hundreds of feet into the air. 

The circumstances leading up to the explosion were unclear. Williams wouldn’t speculate on the cause, only saying that it is under investigation. Williams could not confirm if any surrounding homes had been damaged. 

Sterling is located about 25 miles northwest of Washington, D.C.