Europe's largest atomic energy plant lost power on September 23, the longest of the 10 outages from the grid it has undergone since Russia seized the station following its invasion of Ukraine in February 2022.

Ukrainian President Volodymyr Zelensky on Tuesday said the situation is "critical" at the plant.

Plant management has informed the International Atomic Energy Agency (IAEA) that the site still has fuel reserves for more than 10 days of operation, "with regular offsite supplies maintaining this level", the agency said in a statement.

"While the plant is currently coping thanks to its emergency diesel generators -- the last line of defence -- and there is no immediate danger as long as they keep working, it is clearly not a sustainable situation in terms of nuclear safety," IAEA head Rafael Grossi said in a statement.

"Neither side would benefit from a nuclear accident... I'm in constant contact with the two sides with the aim to enable the plant's swift re-connection to the electricity grid," he added.

Kremlin spokesman Dmitry Peskov told reporters on Wednesday that "the Russian side is ensuring safety at the station."

Moscow and Kyiv have repeatedly accused each other of risking a potentially devastating nuclear disaster by attacking the site and traded blame over the latest blackout.

The plant's six reactors, which before the war produced around a fifth of Ukraine's electricity, were shut down after Moscow took over.

But the plant needs power to maintain cooling and safety systems, which prevent reactors from melting -- a danger that could set off a nuclear incident.

Since the start of the war, Zaporizhzhia has seen multiple safety threats, including frequent nearby shelling, repeated power cuts and staff shortages.

Located near the city of Energodar along the Dnieper river, the power plant is close to the front line.