More than 2,000 residents are being evacuated from four villages in Russian-occupied Crimea after a fire that triggered hours of explosions at a nearby ammunition depot.
Russian-installed officials also shut a stretch of the motorway that crosses the southern half of the peninsula.
They did not explain the cause of the fire at a military training ground near the city of Staryi Krim.
But unconfirmed reports on social media spoke of three Ukrainian strikes.
The Kremlin said Russian President Vladimir Putin had been briefed on the incident.
The overnight explosions coincided with a heavy Russian missile and drone attack that officials said was largely targeted at Ukraine's southern city of Odesa.
Critical infrastructure and military facilities were attacked by several waves of cruise missiles and Iranian-made drones launched from the Black Sea, Crimea and southern Russia, said Ukraine's air force.
Although 37 Russian missiles and drones were shot down, a number did penetrate Ukrainian defences. Officials in Odesa said a number of people were wounded and several flats were damaged. A grain and fuel terminal at the port were hit along with two warehouses including one described as housing fireworks.