More than 12,000 people were evacuated after ammunition stored at the depot near the village of Druzhba began exploding early on Tuesday, sparking a huge blaze.

Security services said they were investigating "possible sabotage" at the facility around 135 kilometres (85 miles) northeast of Kiev, implying Russia's involvement.

Kiev forces have been fighting pro-Russian separatists in the east of the country since 2014 in a conflict that has killed more than 10,000 people.

"Several aircraft have already taken off" to battle the blaze, Ukrainian Defence Minister Stepan Poltorak told a cabinet meeting.

"There is still smoke coming from the arms depot, but I think we will be able to stop it soon," he said.

Poltorak said the depot contained about 70,000 tonnes of ammunition over 680 hectares (1,700 acres), around 43,000 tonnes of which were "ready to use".

There was another powerful blast in the middle of the night, he said, adding that the intensity of explosions on Wednesday was one every three minutes.

"I personally have no doubt that these were attacks on our depots," Poltorak said.

Emergency services said they had no information about fatalities, while regional authorities said more than 60 people required medical help for smoke inhalation.

This was the sixth major fire in three years at a Ukrainian military arms depot.

In March 2017, a huge fire set off explosions at a depot in the town of Balakliya in the Kiev-controlled part of eastern Ukraine, killing one person and injuring five others.

Ukrainian authorities blamed that incident on an "act of sabotage".