Europe faced the prospect of a radiation disaster on Thursday when a Russian-occupied nuclear plant was disconnected from Ukraine's power grid, President Volodomyr Zelensky has said.

It was only due to back-up electricity kicking in that the Zaporizhzhia plant was able to operate safely, he added.

Fires had earlier damaged overhead power lines, cutting the plant off.

There is growing concern over fighting near the complex, which is the largest nuclear plant in Europe.

"If the diesel generators hadn't turned on, if the automation and our staff of the plant had not reacted after the blackout, then we would already be forced to overcome the consequences of the radiation accident," President Zelensky warned on Thursday night.

The damage was caused by fires which Ukraine's state nuclear agency said had interfered with power lines connecting the plant on Thursday, temporarily cutting Zaporizhzhia off from the national grid for the first time in its history.

"As a result, the station's two working power units were disconnected from the network," Kyiv officials said.

Satellite images taken on Wednesday showed an extensive fire burning in the immediate vicinity of the nuclear complex.

President Zelensky blamed the damage on Russian shelling, and in his nightly address accused Moscow of putting Ukraine and Europe "one step away" from disaster.

But local Russian-appointed governor Yevgeny Balitsky blamed the Ukrainian military for the strikes, accusing them of causing power outages to the region as a result.

The BBC was not able to independently verify who was responsible.