Exploding shells set off a fire that triggered more blasts at a military depot in southern Russia, injuring about 30 people and causing the evacuation of more than 6,000 from a nearby village, investigators and emergency workers said.

No cause has yet been determined for the fire at the Chapaevsk military depot in the Samara region on Wednesday. The federal authorities said it was set off by the "involuntary" explosion of shells.

Russian munitions, which frequently date back to the Soviet era, have exploded several times in recent years and the resulting fires usually rage for days. In October a soldier caused a devastating fire at an ammunition depot by dropping a cigarette butt. In other cases shells have exploded during munitions disposal.

The emergencies ministry said about 30 people had sought medical help and 11 of them were taken to hospital, while more than 6,000 people were evacuated from the village of Nagorny. More than 600 emergency workers were trying to put out the fire, the ministry said in a statement posted on its website.

The Interfax news agency said the shells at the Chapaevsk base had a range of less than half a mile.