New fires have broken out in the exclusion zone around the defunct Chernobyl nuclear power plant, which is occupied by Russian forces, according to Ukrainian authorities.

"Significant fires have started in the exclusion zone, which can have very serious consequences," Deputy Prime Minister Iryna Vereshchuk said on Telegram late Sunday.

"However, today it is impossible to control and extinguish fires in full due to the capture of the exclusion zone by the Russian occupation forces."

The International Atomic Energy Agency said on Sunday "the situation remained unchanged" in relation to safeguards at Chernobyl and other nuclear plants in Ukraine.

The UN nuclear watchdog last week said forest fires around Chernobyl did not pose a major radiological risk.

Since March 9 the IAEA has not received live data from Chernobyl. It said Sunday it was concerned about the lack of staff turnover at the plant since March 20.

Russian forces seized the plant on February 24, the first day of the invasion.

Chernobyl's number four reactor exploded on April 26, 1986, causing the world's worst nuclear accident which killed hundreds and spread radioactive contamination west across Europe.

The reactor number four building is now encased in a massive double sarcophagus to limit radioactive contamination.

The original sarcophagus, constructed by the Soviets, deteriorated over the years. A new one was built over it and was completed in 2019.

The plant's other three reactors were gradually shut down after the disaster, the last in 2000.