Russia's leaders have declared a state of emergency in seven provinces and ordered authorities to guard weapons storage facilities from wildfires that have killed at least 40 people.
Thousands more have lost their homes to blazes stoked by Russia's worst heatwave since the Tsarist era.
The heat has parched crops in one of the world's largest grain exporting nations, helping drive global grain prices to 22-month highs.
‘Many families have nothing left - the flames destroyed everything,’ President Dmitry Medvedev said in a sober announcement on state television.
‘It is a huge tragedy.’
With little relief expected this week, he urged Russians to take care in tinder-dry forests and fields, warning that ‘every match tossed away could lead to irreparable disaster’.
Mr Medvedev's emergency decree covers European Russian regions from Voronezh in the south to several Volga River areas and the densely populated province ringing Moscow.
A blanket of acrid smog covered the sweltering capital itself, worsening the woes of Muscovites gasping in Russia's hottest weather since record-keeping began around 1880.
Some wore facemasks to filter the air they breathed.
Prime Minister Vladimir Putin ordered authorities to protect weapons sites, power plants and other vital facilities.
‘The last thing we need is for arms stores to fall into this zone (affected by fires),’ Putin said at a meeting with emergency officials and governors of affected regions.
Authorities said they had increased the number of firefighters near an iconic nuclear research centre by tenfold, but a spokesman for Russia's state nuclear corporation Rosatom, Sergei Novikov, said the centre was not currently in danger.
The facility at Sarov in the Nizhny Novgorod province around 350km east of Moscow was a top-secret location in Soviet times codenamed Arzamas-16, where the first Soviet atom and hydrogen bombs were designed.
‘At the present time, all the fires around (the centre) have been put out so there is no threat to the nuclear centre,’ Novikov said.
‘There may be a threat of further fires from the south but special groups are prepared for that contingency.’
Mr Putin warned that small blazes in areas where fires have been extinguished could be whipped up by winds and spread again. ‘Everything must be put out,’ Mr Putin said.
Temperatures between 35-42 degrees Celsius are expected in Moscow and central Russia over the next few days.
