The Russian capital Moscow has suffered its hottest day on record, with temperatures reaching 39C (102F).
A month-long record-breaking heatwave has sparked nearly 50 fires in the Moscow region and the capital is sweltering under a thick layer of smog.
Health experts say pollution levels in parts of the city are 10 times higher than normal safety limits and advise locals to stay indoors or wear masks.
A state of emergency has been declared in more than 20 drought-hit regions.
It is estimated a fifth of the country's wheat crop has now died due to the lack of rain in what is thought to be the country's worst drought for more than a century.
Scores have died in the heatwave, some drowning having taken a swim after drinking too much vodka.
Emergency aircraft have already dropped several hundred tonnes of water to extinguish the blazes.
But dozens of peat and forest fires are still burning on the outskirts of the capital, says the BBC's Richard Galpin in the city.
Health officials have warned the high concentration of carbon monoxide in the air makes breathing as dangerous as smoking several packets of cigarettes every day.
One of the largest fountains in the capital's centre has been turned into a pool, with some people swimming in their bathing costumes while others are simply jumping in fully clothed.
Prime Minister Vladimir Putin has been asked to commit 25bn roubles ($827m; £531m) towards the emergency effort.
The Roshydromet meteorological service had earlier predicted the smog would begin to clear on Thursday evening, saying temperatures were forecast to cool off over the weekend.