The plant -- Europe's largest -- was seized by Russian soldiers in the opening days of the invasion and has remained on the front line ever since.

This week the facility has come under fire repeatedly, with Kyiv and Moscow trading blame for the dangerous escalation.

The mayor of the southeastern city of Energodar, where the plant is located, said "the risks are increasing every day" as Russian forces are "shelling the infrastructure that ensures the safe operation of the station".

"What is happening there is outright nuclear terrorism," Dmytro Orlov told AFP by telephone from the city of Zaporizhzhia, which remains under Ukrainian control.

"It can end unpredictably at any moment."

Kyiv has accused Moscow of basing troops and weapons in the station, launching attacks and using the atomic plant as a shield from returning fire.

In his televised address Saturday, President Volodymyr Zelensky accused Russia of nuclear "blackmail" and using the plant to "intimidate people in an extremely cynical way".

The UN Security Council held an emergency meeting over the situation on Thursday and warned of a "grave" crisis unfolding in Zaporizhzhia.

"The invaders continue to terrorise the civilian population and the nuclear power plant," said Orlov.

"Fire safety rules are repeatedly violated. The situation is heating up, and the escalation continues."

He said "mortar shelling of the nuclear power plant is carried out every day and night from the occupied villages".

"The situation is hazardous, and what causes the most concern is that there is no de-escalation process," he added.

Orlov also said that over the past 24 hours, Energodar -- which he left at the end of April -- had started to be shelled for the first time, with a dramatic increase in those hoping to evacuate.

He warned that in the "near future" there may not be enough personnel to man the station.

Ukraine was the site of the world's worst nuclear accident in 1986, when a reactor at the Chernobyl plant exploded and spewed radiation into the atmosphere.