An explosion at a U.S. Army depot outside of Tokyo has set off a large blaze that lit up the night sky, but there were no reports of injuries.

The U.S. Defense Department says the explosion happened after midnight in Japan on Monday at the Sagami Depot in Sagamihara, a city about 25 miles (40 kilometers) southwest of Tokyo.

A statement issued by the Army in Japan adds that the cause is unknown, and there are no indications of injuries. The Army says the building was not a hazardous material storage facility, and that the depot does not store ammunition or radiological materials.

A duty officer at the Pentagon says base firefighters and first responders are fighting the fire to prevent its spread to nearby buildings.