Around 12,000 people have been evacuated after a fire and explosions at a rate of two to three a second hit a Ukrainian Defence Ministry ammunition depot, officials say.
No casualties were reported.
Ukraine's defence ministry's spokesman said the fact that explosions were set off in different parts of the depot pointed to sabotage.
The depot is located in the Chernihiv region, 176 km east of the capital, Kiev. A woman who lived 50 km away told the TV channel 112 she could hear the explosions.
"There are no victims, wounded, injured or killed among military personnel, personnel of the Armed Forces of Ukraine and the local population," a Defence Ministry statement said.
The airspace in a 30 km radius was closed and road and rail transport suspended. The emergency services reported gas and electricity supplies to the area have been disrupted.
Hundreds of people and equipment were deployed to the site, a statement by the emergency services said, joined by Prime Minister Volodymyr Groysman and the head of Ukraine's armed forces Viktor Muzhenko. The president has called for a report.
