A state of emergency was declared on Monday in the Russian region of Ryazan, some 200 kilometres south-east of Moscow, due to widespread forest fires.
The fires covered an area of about 9,000 hectares, Russian agencies reported, citing aerial observations by the Forestry Agency.
Acrid smoke from has reached Moscow in recent days, limiting visibility there.
Moscow Mayor Sergei Sobyanin reportedly sent 9,000 relief workers with more than 2,300 vehicles and heavy equipment from the capital to the fire-hit region to support local forces.
Firefighting aircraft and helicopters were also deployed.
The smoke will remain noticeable in Moscow until the end of the working week, meteorologists predicted.
Heat with 30 to 33 degrees Celsius is also expected in the Russian capital at least until Thursday.