Hundreds of firefighters on Monday battled a forest blaze in Ukraine’s Chernobyl exclusion zone while officials insisted there was no risk to the ruined reactor and nearby storage facilities for nuclear waste.

“There is no threat to the Chernobyl nuclear power plant and the storage facilities,” Volodymyr Demchuk, a senior official from Ukraine’s emergency service, said in a video statement late on Monday.

The fire broke out 10 days ago at the scene of the world’s worst nuclear accident in 1986.

Kiev has mobilised helicopters and more than 400 firefighters, with planes dropping tonnes of water on the fire.

Demchuk said firefighters are now focused on stopping the spread.

While forest fires are common in the exclusion zone, Greenpeace Russia said on Monday that this is the worst since the 1986 nuclear explosion.

The environmental campaign group said that analysis of satellite images showed the fire at its closest point was just 1.5km from the protective dome over the ruined reactor.

Regional Eastern European Fire Monitoring Centre head Sergiy Zibtsev told AFP that the fire is “super-huge” and “unpredictable”.

“In the west of the exclusion zone it has already covered 20,000ha by our calculations.”

The Ukrainian emergency service has not provided recent figures on the size of the fire.

Association of Chernobyl Tour Operators head Yaroslav Yemelianenko said the fire had reached the ghost town of Pripyat, a city near Chernobyl whose population of around 50,000 was evacuated after the explosion.

Pripyat has become popular with tourists from all over the world.

“The situation is critical,” Yemelianenko wrote on his Facebook page.

However, Ukrainian Deputy Minister of Internal Affairs Anton Gerashchenko said there is no danger for the nuclear waste storage facilities. “It’s completely safe,” he said on Facebook.

The fire broke out on April 4 in a forested area near the Chernobyl power plant.

Police said the blaze was started by a man burning dry grass near the exclusion zone around the ruined reactor.

The flames spread quickly, fanned by strong winds, and Kiev began deploying helicopters and firefighting planes.

Government agencies have insisted the fire has not caused a rise in radiation levels.

Yegor Firsov, head of the Ministry of Environment and Natural Resources’ State Ecological Inspection Service, wrote on Facebook a day after the fire broke out that levels at the centre of the fire were higher than normal. He later withdrew the claim.

Chernobyl polluted a large swathe of Europe when its fourth reactor exploded in April 1986.

People are not allowed to live within 30km of the power station.

The three other reactors at Chernobyl continued to generate electricity until the power station finally closed in 2000. A giant protective dome was put in place over the fourth reactor in 2016.