The first explosion was heard at around 6:00 pm (1100 GMT) at a depot used to store expired ammo inside a military complex, in West Java near Jakarta.

"At 6:05 pm, smoke was spotted in (a) warehouse... and there were explosions," Jakarta city military chief Mohamad Hasan said during a televised press conference.

Authorities evacuated nearby residents to safer areas as fire tore through the storage facility, the military commander said.

"We assure you there is no fatality at the moment but we cannot enter the location because there are still minor explosions," he said.

The military received reports that shells or projectiles might have landed in the surrounding areas and urged people not to touch the objects.

Hasan said the exploded warehouse had no electricity and the explosion might have been caused by unstable expired ammunition.

"We suspect this (the explosion) was caused by expired ammunition," Hasan said.

"It is possible that the chemical and explosive material was unstable."