Around 12,000 people were evacuated after a defence ministry ammo depot near the town of Ichnya, in the Chernigov region, blew up. There were two to three explosions a second.
Ukraine Armed Forces said the explosion occurred at 3:30am local time. Ukraine's state security service said it was investigating possible sabotage, and the defence ministry's spokesman said the fact that explosions were set off in different parts of the depot pointed to sabotage.
220 rescue workers and 60 technical units were deployed urgently to the scene. No casualties were reported.