Kiev (AFP) - A forest fire broke out Tuesday near the Chernobyl plant in Ukraine, scene of the world's worst civil nuclear disaster in 1986, but posed no danger to the site, officials said.

"The fire is at a distance of 15 to 20 kilometres (9 to 12 miles) from Chernobyl," Maya Rudenko, a spokeswoman for the plant, told AFP by telephone, adding there was "no problem" there.

Interior Minister Arsen Avakov warned however that "the high flames and sudden gusts of wind mean there is a serious risk that the fire could spread."

The area around Chernobyl was evacuated after the 1986 blast and the last reactor there shut down in 2000 but some personnel still operate in the exclusion zone, where work is underway to lay a new seal over the reactor site.

Avakov said the fire had spread over some 400 hectares near the plant, which lies around 100 kilometres (62 miles) from the Ukrainian capital Kiev.

Around 200 firefighters with scores of vehicles were battling the inferno and aircraft were dumping water on the flames, the state emergency services said.

They said the fire started shortly after noon (around 0915 GMT).

- Radiation level unchanged -

Ukraine's Prime Minister Arseniy Yatsenyuk visited the area on Tuesday afternoon and met with emergency workers.

"The situation is under control," he told reporters at an air base where firefighting craft were taking off from.

"Our emergency services are actively working to stop the fire spreading."

A state nuclear inspection official told AFP that "the level of radiation at the Chernobyl plant has not changed".

The fire comes just two days after Ukrainians marked 29 years since the Chernobyl nuclear disaster.

The explosion of reactor number four on April 26, 1986, spewed poisonous radiation over large parts of Europe, particularly Ukraine, Belarus and Russia.

The human toll of the disaster is still disputed.

United Nations experts officially recognised 31 deaths among plant workers and firefighters directly linked to the blast.

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But environmental group Greenpeace has suggested there could be around 100,000 additional deaths from cancer caused by the disaster.

The Soviet authorities of the time dispatched hundreds of thousands of people to put out the fire and clean the site, without proper protection.

They hastily laid over the reactor site a concrete cover dubbed "the sarcophagus", which is now cracking and must be replaced.

Ukraine's President Petro Poroshenko on Sunday inspected ongoing work on a new 20,000-tonne steel cover -- a project estimated to cost more than two billion euros ($2.2 billion).

It is financed by international donations managed by the European Bank for Reconstruction and Development (EBRD).

The structure will contain technology that will act beneath the cover to decontaminate the area once the steel layer is in place. Officials say the new cover will last for 100 years.

The work is being done by Novarka, a joint venture by French companies Vinci and Bouygues.

The project had been scheduled for completion by the end of this year but the EBRD said last year technical problems would delay it until late 2017.