Security services said they were investigating "possible sabotage" in the incident at a defence ministry depot near the village of Druzhba, around 135 kilometres (84 miles) northeast of Kiev.

Emergency services said they had no information on any deaths, and regional authorities said more than 60 people required medical help for smoke inhalation.

Grey and white smoke rose up from the horizon on Tuesday morning, an AFP photographer saw, while explosions were going off every one to two minutes.

A defence ministry official said the fire was raging in five storage areas, covering about 10 percent of the total of about 700 hectares (1,700 acres).

The fire and explosions began around 3:30am local time (0030 GMT) at the Number Six depot, the emergency services said.

Four explosions went off in different parts of the depot before a fire broke out, the deputy head of Ukraine's General Staff, Rodion Tymoshenko, said, suggesting this meant the incident could be "sabotage," a thinly veiled jab at Russia.

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.

More than 12,000 people were evacuated from the area at risk, the emergency services said.

President Petro Poroshenko called a meeting of the heads of security forces and promised to give residents all the necessary help, his spokesman wrote on Facebook.

Prime Minister Volodymyr Groysman travelled to the scene and chaired a meeting of emergency services officials.

"The main thing is to preserve people's lives. Whatever's destroyed, we will rebuild," he wrote on Facebook.

Authorities closed the airspace in a 30-kilometre radius around the site, as well as rail and road traffic.

More than a hundred firefighters worked at the scene, while the defence ministry sent in a firefighting tank.

- 'Possible sabotage' -

The defence ministry said the intensity of the explosions had lessened in the morning and that the current explosions were from rifle ammunition, not shells.

Tymoshenko denied a claim by the emergencies service that the depot contained 88,000 tonnes of ammunition, while saying the real total was a secret.

More than half the ammunition was safely removed from the depot before the fire broke out, he said at a briefing.

The SBU security service said it was looking into "possible sabotage."

Military prosecutors opened a probe into possible negligence by officials.

Stockpiles of outdated ammunition dating back to the Soviet era often cause fires and explosions in Ukraine and Russia.

This was the sixth major fire in three years at an arms depot of the Ukrainian army.

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".

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