Russia has sent a special firefighting train to join over 3,400 firefighters battling to douse wildfires close to its top nuclear research centre, officials said.

While no blazes had been registered on the territory of the nuclear research centre in Sarov in central Russia itself, a nearby nature reserve has been on fire for around a week.

Authorities are today boosting firefighting teams to more than 3,400 people to keep the fire from spreading to Sarov, a town in the Nizhny Novgorod region still closed to foreigners as in Soviet times.

The nature reserve is located in nearby region of Mordovia and tree leaves and pine needles on the surface -- and not the trees themselves -- now are burning and smouldering, said Mikhail Turkov, a spokesman for the emergencies ministry's Volga regional branch.

"Two planes and two helicopters are currently circling over Sarov," Turkov told AFP. "Reconnaissance is being constantly conducted from the air."

More than 3,400 people and a firefighting train were involved in putting out the fires, while a second train was currently on its way to the scene. The firefighting trains contain vast amounts of water and special hoses.

A new fire in the area broke out late Wednesday when lightening hit a pine tree, the local emergencies ministry said.

A spokeswoman for the Sarov nuclear center confirmed to AFP there were no fires on the centre's territory and said its staff was not being evacuated. She declined to give further details.

Two soldiers were killed by blazing trees as they strove to put out a fire close to the centre on Monday.

Russia is battling what experts say is the worst heatwave in its millenium-long history which has affected nearly all areas of life and may shave off one percent from Russia's gross domestic product, according to some estimates.

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