Staff were disposing of Russian anti-aircraft shells out of production since 2014 when a box was dropped and exploded, the Times of India reported.

"While the workers were unloading a crate of ammunition it bumped on the ground, triggering an explosion which killed four of them on the spot. Two others died on their way to the hospital," senior officer Nikhil Pingle told AFP.

Ten others were injured in the blast in the town of Pulgaon in Maharashtra state.

India's armed forces have a history of fires and other accidents which are often blamed on lax safety standards.

Two years ago a blast at the same facility in Pulgaon killed 18 people, including two senior army officers.

The depot, one of the country's largest that stores bombs, grenades and other ordnance, was built during World War II.

In 2013, a fire on the submarine INS Sindhurakshak in Mumbai sank the vessel and left 18 sailors dead.