TOKYO -- Four people were injured after an explosion occurred Monday within the US military's Kadena Air Base in Japan's southernmost prefecture of Okinawa, local media reported.

The blast went off at an ammunition depot that belongs to Japan's Self-Defense Forces (SDF), public broadcaster NHK reported, citing SDF sources.

At around 11:20 am local time, the fire department received reports about the explosion at the SDF-managed facility when the SDF personnel were preparing to carry out bomb disposal operations.

Four SDF members working at the depot were taken to hospital following the incident, suffering injuries including burns to their fingers, the report said.

None of the injured are in critical condition, it added.

Police are currently investigating the situation at the scene. No evacuation order has been issued for nearby residents.