One person has been killed following a series of blasts at a Russian military air base close to seaside resorts on the annexed Crimean peninsula.
Witnesses said they heard at least 12 explosions at about 3.20pm local time (1.20pm BST) from the Saky base on the west coast.
There was speculation that the base had been hit by missiles but Russia said ammunition had detonated.
Videos posted on social media showed people fleeing a beach as flames and pillars of smoke rose up from multiple locations.
Witnesses also reported a fire on a runway and damage to nearby homes, Crimea Today News said on Telegram.
Crimea's health department said one civilian had been killed, while another person had been treated in hospital for moderate injuries and a further five suffered minor wounds.
Russia annexed Crimea from Ukraine in 2014 and used it as a launchpad for the invasion of its neighbour in February.
Russian warplanes have used the base to strike areas in southern Ukraine.
Moscow said the explosions were detonations of stored ammunition, and had not been caused by an attack.
Russia's main news agencies quoted an unnamed ministry source as saying that "only a violation of fire safety requirements is considered as the main reason for the explosion of several ammunition stores at the Saky airfield".
The source added: "There are no signs, evidence or, even less, facts (to indicate) a deliberate impact on ammunition stores."
There were suggestions on Ukrainian social media, however, that the base had been hit by long-range missiles fired from Ukraine.
In an apparently sarcastic post on Facebook, the Ukrainian defence ministry said: "The Ministry of Defence of Ukraine cannot establish the cause of the fire, but once again recalls the rules of fire safety and the prohibition of smoking in unspecified places."
It added: "We can't rule out that the occupiers will 'accidentally' find some characteristic 'insignia', 'visiting card' or even 'DNA'."
Since the war began, Russia has reported numerous fires and explosions at munitions storage sites on its territory near the Ukrainian border, blaming some of them on Ukrainian strikes.
Ukraine has mostly not commented.