An explosion occurred today just after midnight Japan time at a building on a U.S. Army post, the Sagami Depot in the city of Sagamihara, Japan, military officials said.

There were no indications of anyone being injured, and base firefighters and first responders fought the resulting fire to keep it from spreading to nearby buildings, according to a PACOM spokeswoman.

The cause of the explosion was not known, the spokeswoman said. The building that exploded was not a hazardous material storage facility, but investigators were in the process of determining the contents of the building, she said. The depot does not store ammunition or radiological materials.