A fire that broke out at the military training grounds in the Kirovske district on the Crimean Peninsula has forced the evacuation of more than 2,000 people and a closure of nearby highway, the Moscow-backed governor of Crimea said on Wednesday.

"It is planned to temporarily evacuate residents of four settlements - this is more than 2,000 people," Russian-installed Governor Sergei Aksyonov of Crimea said on the Telegram messaging app.

There was no reason given for the fire, which also forced the partial closure of the major Tavridy Highway.

Russia's Telegram channels linked to Russian security services and Ukrainian media reported that an ammunition depot was on fire at the base after Ukrainian overnight air attack.

Reuters could not independently verify the reports. There was no immediate comment from Ukraine.

Serhiy Bratchuk, spokesperson for the Odesa military administration in Ukraine posted two videos of a fire in an uninhabited area, saying, "Enemy ammunition depot. Staryi Krym."

Staryi Krym is a small historical town in the Kirovske district of Crimea. Russia annexed the Crimean Peninsula from Ukraine in 2014.

Social media videos and photos showed big flames and a smoky fire in an uninhabited area, broken by series of detonations. Some Telegram channels said that by 0730 local time (0430 GMT), the fire was going on for about three hours, still not being contained.

The fire comes two days after a blast damaged a bridge linking Russia to the Crimean Peninsula on Monday that Moscow blamed on Ukraine and for which President Vladimir Putin vowed retaliation.

Overnight, Russia launched an air attack on the Ukrainian port of Odesa for a second night in row. Ukraine's military also said that a drone attack at Kyiv was successfully repelled early on Wednesday.