"On normal days, between 360 and 380 die. Now it's around 700," Moscow's health chief, Andrei Seltsovsky, told the Interfax news agency, according to several media reports.
The capital has 1,500 places available in its morgues, and 1,300 of them are now filled, he said, blaming the heat wave and pollutants for the deaths.
Residents were told to stay away from the region's picturesque woodlands until further notice. An explosion at the Mayak plutonium-producing plant there in 1957 (when it was still known as Chelyabinsk) killed hundreds of people and contaminated large areas with radioactive waste.
Russian officials on Friday voiced similar concerns that the fires could stir up contamination from the Chernobyl disaster in 1986, but no further word has been issued. At the same time the Defense Ministry ordered missiles moved from a depot outside Moscow.
Soon after Seltsovsky's announcement, Russian Health Minister Tatyana Golikova said she was "puzzled by the unofficial figures quoted at the briefing" and demanded clarification, the BBC reported.
But as the heat wave continued, the Russian capital was covered for a sixth straight day by smog from nearby peat bog fires, leading more than 104,400 people to flee Moscow by air Sunday, Bloomberg News said. They joined 95,000 people who left Saturday, according to the Federal Air Transportation Agency.
Conditions in the city have reached the point where carbon monoxide and airborne pollutants are at least twice the levels deemed safe.
Today the head of the state weather service, Alexander Frolov, said the heat wave was the worst in 1,000 years of recorded Russian history, with temperatures above 95 degrees forecast for Moscow until Thursday.
A total of 557 wildfires continued to blaze today in Russia, mostly in the west, the emergencies ministry said, 25 of them burning peat bogs, and 10,000 firefighters are backing up soldiers trying to bring the blazes under control. The ministry said the death toll is at least 52.
Public criticism of the government's response to the fires has been high. Reuters reported that a Moscow doctor wrote on a now-deleted Internet blog Sunday that he was hesitant to diagnose people with heat-related illnesses for fear he would be fired.
The doctor, who was not identified, said the refrigerators at his clinic were full of dead bodies, leaving a "rotting stench." Further bodies of people who had died from heatstroke and smoke-induced illnesses were piling up in the basement, he said.