Both sides said there had been no detected spike in radiation levels around the power station, which has been under the control of Russian forces since the first days of its full-scale military offensive.

"As a result of shelling of the town of Energodar by the Ukrainian armed forces, there was a fire at a cooling system of the Zaporizhzhia nuclear power station," Yevgeny Balitsky, the Russian-installed governor of Ukraine's Zaporizhzhia region said on Telegram.

Ukrainian President Volodymyr Zelensky said in a social media post "Russian occupiers have started a fire" at the plant.

"Currently, radiation levels are within the norm," he added.

Balitsky also reported the "radiation background" around the facility was normal.

Ukraine's interior minister said it was "intensively monitoring" the situation from meterological stations near the plant, which is Europe's largest nuclear power station.

All six of its units are currently in cold shutdown, Balitsky said.

"There is no threat of a steam explosion or any other consequences," he said, adding that firefighters were on site battling the blaze.

A video published by Zelensky showed black smoke billowing out of one of the station's cooling towers as red flames licked around the bottom.

The site is on the eastern bank of the Dnipro river -- a de facto frontline snaking through southern Ukraine.

Ukraine controls the opposite bank and Russia has repeatedly accused its forces of deliberately shelling the plant -- claims denied by Ukraine.

Kyiv, in turn, has accused Moscow of militarising the facility, including by placing heavy weapons there at the start of the conflict.

Russia's control over the plant is a form of nuclear "blackmail", it says.

The International Atomic Energy Agency (IAEA), which has staff stationed there, has repeatedly urged restraint, saying it fears reckless military action could trigger a major nuclear accident at the plant.