Ukrainian authorities say a wildfire has broken out in the exclusion zone around Chernobyl, where the world's worst nuclear accident occurred in 1986, but radiation levels remained within safe limits.

"Radiation levels have not risen either inside the exclusion zone or in adjoining areas," the zone's administration said in a statement on June 5.

Prime Minister Volodymyr Hroysman wrote on Facebook that "radiation levels are safe. In Kyiv and in Chernobyl itself, including at the Chernobyl power station site, they are significantly below the acceptable limits. So there's no need to worry."

"I stress once more: the situation is fully under control," he added.

The fire broke out in dry grass on the morning of June 5 in the area of high radiation less than 10 kilometers from the power station, and later spread over some 10 hectares of woodland, the state emergency service said in statements.

It published photographs of smoke billowing from woodland and flames spreading along the ground.

The state nuclear-industry regulator said the former nuclear power station was not at risk from the flames.

More than 130 firefighters were battling the fire as well as two planes and a helicopter that dumped water on the fire, the state emergency service said, adding that the wind was not blowing toward the capital, Kyiv.

Wildfires occur regularly in the woods and grassland around the power station. In 2015, a forest fire burned for four days.

Chernobyl's No. 4 reactor, which is about 100 kilometers north of Kyiv, exploded in 1986 during testing in the worst such accident ever.

Radioactive fallout from the power station contaminated up to three-quarters of Europe, according to some estimates, with Ukraine, Russia and Belarus, all then part of the U.S.S.R., the worst affected.

A 30 kilometers radius around the power station is still an exclusion zone where people are not allowed to live.

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.

With reporting by AFP and TASS