Tourists with face masks walk through thick smog in Moscow's Red Square on Monday. (Alexander Zemlianichenko/Associated Press)

Deaths in Moscow have doubled and are now averaging 700 people a day amid a sweltering heat wave and poisonous smog from wildfires, a top Russian health official said on Monday.

Moscow health chief Andrei Seltsovky blamed weeks of unprecedented heat and suffocating smog for the rise in mortality compared with the same time last year, Russian news agencies reported.

He said city mortuaries are close to their capacity, with 1,300 bodies.

Acrid smog blanketed Moscow for a sixth straight day on Monday, with concentrations of carbon monoxide and other poisonous substances two or three times higher than what is considered safe.

Those airborne pollutants reached a record over the weekend — exceeding the safe limit by nearly seven times.

"The best way is to leave Moscow, to a dacha or elsewhere, the farther the better," one Muscovite, Viktor Kanygin said.

About 550 separate blazes were burning nationwide on Monday, mainly across western Russia, including about 40 around Moscow, according to the Emergencies Ministry.

Forest and peat bog fires have been triggered by the most intense heat wave in 130 years.

Daily highs have reached up to 38 C, compared with the summer average of 24 C, and according to the forecast, there will be no respite this week.

At least 52 people have died directly in the wildfires and over 2,000 homes have been destroyed. Flights to Moscow have been delayed and diverted.

Russian authorities have acknowledged that the 10,000 firefighters battling the blazes aren't enough, and sent thousands of soldiers to help fight the fires.

Neighbouring Ukraine is also battling with fires as it suffers its worst heat wave on record.

On Sunday firefighters in Dnepropetrovsk region, aided by soldiers, battled blazes in Novomoskovsky district.

Temperatures have soared to 42 C in Ukraine's eastern, central and southern regions, with minor wildfires across the country.

President Viktor Yanukovych interrupted his holiday in the Crimea to monitor the situation.

Forecasters predict at least two more weeks of high temperatures.