Europe's largest nuclear power plant needs a reliable electricity supply to operate pumps that circulate water to cool reactors and pools holding nuclear fuel.

Since a Russian strike on March 9, the plant has relied on a single backup power line that remains "disconnected and under repair", according to Rafael Grossi, head of the International Atomic Energy Agency.

"Nuclear safety at the ZNPP remains in a precarious state," Grossi said in a statement on Wednesday.

The plant's lack of access to the grid and necessary repair work on its last emergency power line could cause a complete loss of power, making it reliant on diesel generators for the seventh time since Russia captured it a year ago, Grossi said.

"I once again call for a commitment from all sides to secure nuclear safety and security protection at the plant."

Emergency diesel generators had been activated to power the plant's safety systems, according to Ukrainian nuclear energy agency Energoatom, which has warned of the risk of an accident.

Without the electricity produced by these generators, the overheating of the reactor fuel could cause a nuclear accident, as in Japan's Fukushima in 2011.

The plant was cut off from the Ukrainian power grid for 11 hours following the Russian strike. Both sides have accused the other of shelling in the vicinity of the plant since its occupation by Moscow's troops at the war's beginning.

The strike came during a fresh wave of Russian attacks across Ukraine which killed at least nine people and led to power outages across the country.

Ukrainian President Volodymyr Zelensky said he discussed the situation at the plant with visiting Japanese Prime Minister Fumio Kishida.

"We discussed how to find a more effective mechanism for the de-occupation of our nuclear plant," Zelensky told reporters on Tuesday.

"Because the format in which we live, with all respect and gratitude for what Mr. Grossi is doing to resolve this situation, does not help the Zaporizhzhia station, no international institution is able to solve this issue."