Weather forecasters said Russia's worst heatwave in decades would continue for the next few days.
"I can't bear it any more," said Anna Kozyreva, 25.
"My parents have left the city. All I want to is breathe normally, but my job doesn't allow me to leave."
Some Russians have complained of severe eye irritation, and have been forced to cover their noses and mouths in wet fabric to try to filter the air.
A NASA satellite image of the smoke from forest and peat fires swirling over Russia.
A Nasa satellite image of Russia shows swirling smoke drifts
"The smoke is everywhere - at home, in shopping malls, on the subway," said Roman Morozov, a 29-year-old architect.
Landmarks, including the Kremlin, disappeared behind a layer of smoke and dozens of flights bound for Moscow'sDomodedovo and Vnukovo airports have been diverted or delayed.
Some are being sent to Sheremetyevo airport, north of Moscow, where smog is not so dense, but other flights were rerouted as far away as Ukraine.
"It's hellish, all the flights are delayed or cancelled. There are thousands of passengers waiting in the heat and smog and the air conditioning isn't working," a passenger trying to flee via Domodedovo told AFP by telephone.
The smoke comes from a total of more than 600 forest and peat fires, making more than 4,000 people homeless and killing at least 52 others.
"The situation is truly extreme. People are in circumstances under which they should not have to live," leading Russian doctor Ivan Yurlov, of the League for the Nation's Health, said.
L-Russia1
Both residents and tourists have resorted to face masks
Package tours have sold out as residents try to depart the country, adding to the woes of dozens of delayed and cancelled flights.
Russian commentator Alexander Nekrassov told Sky News that the city's top official was ignoring residents' pleas for help.
"The mayor of Moscow is on holiday and and said he is not going to cut it short," Mr Nekrassov explained.
"Moscow is one of the most polluted cities in Europe, if not the world."
Authorities have tried to calm citizens, especially after some of the nation's nuclear facilities were threatened.
The smoke is everywhere - at home, in shopping malls, on the subway
Roman Morozov, a 29-year old resident of Moscow
"The fire situation in the Moscow region is still tense, but there is no danger either for residential areas or for economic sites," an Emergencies Ministry spokesman said.
The air pollution surged after Russia's worst heatwave in over a century began a month ago, Moscow's pollution monitoring agency said.
Officials have suggested Muscovites stay indoors because of hazardous levels of carbon monoxide and fine particles in the air.
The Foreign Office has warned visitors about the Moscow smoke and advised intending travellers to check with airlines before leaving for their departure airport.