A U.S. Army depot building in Japan exploded just after midnight local time on a base about 25 miles southwest of Tokyo, U.S. military officials said.
The Army does not know what caused the fiery incident in the city of Sagamihara, but no injuries were reported.
Photos and video of the event quickly rippled across social media with posts on Twitter, Facebook, and YouTube of a thunderous explosion followed by a ball of fire that lighted up the night sky.
U.S. Pacific Command, which oversees U.S. military operations in the region, confirmed the explosion happened at Sagami general depot early Monday morning.
Commander Ivy Kupac, Pacific command spokeswoman, said in a statement that the depot did not store ammunition or radiological materials.
"The building that exploded was not a hazardous material storage facility," she said. "We are in the process of determining the contents of the building."
The Army's Sagami general depot is home to the 35th Combat Sustainment Support Battalion, which provides combat service and logistics support throughout the region.
The battalion provided humanitarian assistance and disaster relief to victims of the Japan's deadly 2011 earthquake and tsunami by cleaning up transportation hubs and issuing food, fuels, transportation and shower support.