Around 10,000 people were evacuated after a fire and explosions hit a Ukranian Defence Ministry ammunition depot 176km east of the capital Kiev early on Tuesday morning, officials said.
There was no mention of any casualties and it was not immediately clear whether the explosions were an accident or sabotage.
The airspace in a 20km radius has been closed and road and rail transport suspended. Hundreds of people have been deployed to the site, a statement by the emergency services said, and the head of Ukraine’s armed forces has gone there.
There have been several large fires at ammunition and weapons depots in recent years, an additional drain on Ukraine’s military, which has been fighting Russian-backed separatists in eastern regions since 2014.
“About 10,000 people were evacuated,” the statement by the emergency services said. “From 4:22am (0122 GMT) the airspace within a radius of 20km has been closed. The movement of rail and road transport is suspended.”
Last year massive explosions at a military depot in the Vynnytsya region, 270km west of Kiev, forced the authorities to evacuate 24,000 people.
