MOSCOW Dense clouds of acrid smoke from peat and forest fires choked Russia's capital on Friday, seeping into homes and offices, diverting planes and prompting exhausted Muscovites to wear surgical masks to filter the foul air.
Air pollution surged to five times normal levels in the city of 10.5 million, the highest sustained contamination since Russia's worst heatwave in over a century began a month ago.
"It feels like I'm in a burning house and I can't escape," said Yelena Petrenko, 32, who used a handkerchief to cover her mouth because drugstores she visited had run out of facemasks.
Officials urged Muscovites to stay indoors because of the dangerous levels of carbon monoxide and fine particles in the air. Weather forecasts said the smoke, which has reached even underground metro stations, would persist until Monday.
On Red Square, smoke shrouded the onion domes of St Basil's cathedral. The weekly changing of the guard ceremony in the Kremlin was canceled for Saturday.
NASA satellite images showed a 3,000 km-long (1,850 mile) smoke cloud covering swathes of European Russia.
Moscow temperatures reached 36 Celsius (96.8 Fahrenheit) on Friday, breaking a daily record for the fifth straight day.
The deadliest wildfires in nearly four decades have killed at least 52 people and left more than 3,500 homeless as entire villages of wooden homes burned down, official figures say.
The true toll from the smoke and heatwave may be much higher. Interfax news agency quoted an "informed source" on Friday saying death rates in Moscow surged nearly 30 percent in July because of the "disastrous heat and smoke cloud".
Moscow Mayor Yuri Luzhkov has been silent on the smoke engulfing his city. A city government spokeswoman said he had left on holiday earlier in the week.
One of the world's top grains producers, Russia has announced a temporary ban on exports after crops were ravaged by the dry weather. The news sent world wheat prices soaring.
Despite a huge effort involving more than 160,000 people fighting fires, authorities appeared to be losing the battle.
The size of peat fires burning in the Moscow region almost doubled from 37.5 hectares on Thursday to 65.7 hectares on Friday, the regional Emergencies Ministry branch said.
The emergency has prompted the country's enfeebled opposition to complain of poor fire safety readiness and a slow, ineffective government response.
President Dmitry Medvedev visited an ambulance station in Moscow on Friday and expressed solidarity with smoke-choked Muscovites.
"I woke up this morning and looked around -- it's a monstrous situation," Medvedev said. "Have patience, because I hope this will all end."
Russia's state-controlled media have been at pains to show a vigorous government effort to fight the blazes and have avoided detailed reporting on the hazards to health.
Prime Minister Vladimir Putin has toured fire-stricken regions promising generous compensation to residents and ordering officials to step up efforts to extinguish the blazes.
The government has warned that the fires could pose a nuclear threat by releasing radioactive particles buried in trees and plants by the 1986 Chernobyl nuclear disaster.
A senior Emergencies Ministry official, Vladimir Stepankov, said the most difficult fire situations were in the regions ringing Moscow and Nizhny Novgorod, including the closed town of Sarov, home to a nuclear arms facility.
Russia's nuclear chief on Thursday assured Medvedev that all explosive and radioactive material had been removed.
Sarov's firefighting headquarters said firefghters were trying to extinguish two blazes inside the perimeter of the closed city on Friday, while soldiers cut firebreaks in a burning forest to the south, state-run news agency RIA reported.
The first Soviet nuclear weapon was made in 1949 in Sarov at the Institute of Experimental Physics, which remains the main nuclear design and production facility in Russia.
With visibility low, Russia's aviation authority said at least 60 planes had been diverted to as far away as Ukraine from Moscow's busy airports. Flights and trains out of Moscow were booked solid as residents tried to flee the smoke.
Office workers were sent home as smoke crept into buildings. A spokesman for Russia's No. 1 retailer X5 said all 1,500 staff were ordered home.
"I can smell smoke right here in the office," an employee at a bank, speaking on condition of anonymity, told Reuters.
A trader at another bank said smoke had entered the building and staff were given permission to leave. (Additional reporting by Alexei Anishchuk, Nastassia Astrasheuskaya, Maria Plis, Dmitry Sergeyev and Andrey Ostroukh; writing by Amie Ferris-Rotman, Michael Stott and Steve Gutterman; Editing by Alison Williams and Mark Heinrich)