RT.com reports that the explosions occurred before 1:00 a.m. local time and no evacuations were requested.
Sagami Depot is a post for the U.S. Army's 35th Combat Sustainment Support Battalion. It conducts depot operations and combat service support for the region according to their website.
In April, three explosions were reported near Camp Zama which is less than 10km from the depot. According to the Wall Street Journal, Japanese police believe that left-wing extremists were to blame for that incident.