Amateur video from mobile phones recorded numerous blasts at a military depot in southern Russia where up to 13 million shells were said to have been stored.
At least 6,000 people had to be evacuated from the nearby village of Nagorny in Samara. At least eight people have been reported missing.
Around 500 firefighters were called in to try to put out a fire on the base.
There have been several such incidents in Russia at bases where stored, unstable munitions often date back to the Soviet era. The fires they can trigger sometimes rage for days.
In this case at least 30 people were injured, many of them by flying glass.