A series of explosions hit a munitions depot in eastern Ukraine overnight, the military said Thursday, blaming the incident on an "act of sabotage".

"A fire broke out ... as a result of an act of sabotage at a depot in the town of Balakliya where missiles and munitions were kept," Ukraine's Chief Military Prosecutor Anatoliy Matios said in a statement. "The fire led to the detonation of munitions."

Authorities said Thursday morning that there appeared to be no casualties in the explosions and that some 20,000 people living in a five-kilometre radius were being evacuated from the area.