Ukrainian investigators are calling an explosion at an ammunition dump “subversion”, and have opened an inquiry into the blast. The first explosions were heard late on Tuesday night.

Around 10% of all the storage facilities are on fire at vast site which sprawls over more than half a square kilometre, and has a capacity of 188,000 tonnes of ammunition.

Two people are reported to have been injured. More than 30,000 people were evacuated from around the area. All nearby roads are have been blocked, and electricity and gas lines have been switched off.

The airspace is closed over a 50 km radius. Some 700 soldiers, police and rescue workers and 149 vehicles are trying to supress the fire.