Muscovites struggled to breathe on Monday and Red Square was blanketed in smoke as a record-setting heat wave that has already ruined crops caused fires that set the area around the capital ablaze.
The Emergency Situations Ministry said 34 peat fires and 26 forest fires were blazing Monday in the Moscow region, covering 59 hectares. Experts warned that the air had become dangerous.
Airports serving Moscow were unaffected by the thick smoke, whose sharp, cinder-filled smell permeated the city and crept into offices, homes and restaurants via windows and doors.
"This is awful. It is going to damage people's health," said telephone engineer Davit Manukov, 25, standing by the Kremlin where black clouds of smoke enveloped its golden onion domes.
The Emergency Situations Ministry said it was the worst such attack since a smog outbreak in 2002, which was also a result of smoke from fires caused by hot weather.
The Moscow government agency overseeing air pollution, Mosekomonitoring, said the amount of harmful impurities in Moscow's air exceeded the norm by five to eight times.
"The ecological situation in Moscow has become unfavorable," its chief specialist, Alexei Popikov, said by telephone, adding that it would last several days.
The elderly and those suffering from heart disease should try to avoid contact with the smog, Popikov said, adding that the levels of carbon monoxide and nitrogen oxide were high.
The Emergency Situations Ministry appealed to residents and vacationers to stay away from forests, saying it was unsafe.
Last Thursday, temperatures in the capital hit 35 degrees Celsius for the first time since 1981 as a heat wave that has destroyed Russian crops over an area the size of Portugal showed no sign of abating.
Moscow temperatures are expected to reach all-time highs of 38 to 39 C this week.