"The IAEA Director General and his team have arrived at the ZNPP," Mikhail Ulyanov, Russia's permanent representative to the international organisations in Vienna, said in a tweet.

Grossi, head of the International Atomic Energy Agency, was initially expected to tour the site Wednesday to assess potential safety risks after the destruction of the Kakhovka dam, the source of cooling water for its reactors.

But the visit was delayed to Thursday due to security reasons.

"It was not easy to arrange such a visit under the circumstances, but the Russian side did its best," Ulyanov said.

Since the conflict's start Grossi has warned of the potential for a nuclear accident at the plant, where a permanent IAEA team is based.

The breach of the Russian-held dam, which sits on the Dnipro river and formed a reservoir to provide cooling water, has exacerbated long-running concerns over the facility.

The IAEA has warned that the Kakhovka dam disaster, which sparked mass evacuations, further complicated "an already precarious nuclear safety and security situation" at the plant.

Grossi's visit follows a meeting with Ukraine's President Volodymyr Zelensky in Kyiv on Tuesday.

Grossi has visited the plant twice since it has been occupied by Russia, whose forces seized it over a year ago.