Muscovites have been warned to stay indoors and wear protective masks owing to the thick smog that continues to engulf the Russian capital.
Health officials say carbon monoxide levels are more than six times greater than the norm.
The wildfires around Moscow have claimed 52 lives and hospitalised dozens more.
Russia is currently sweltering under its worst heat waves in decades and forecasters warn there is little respite in sight with more hot weather on the way.
Scores of flights at the city’s Sheremetyevo airport were grounded because the runways were shrouded in smog.
Alexander Neradko, head of Russia’s Air Transportation Agency, said: “Our job is to guarantee the safety of each flight. All crews have been reminded of the strict standards we apply in this situation. Planes should not land in conditions which do satisfy the minimum amount of visibility required to do so safely.”
Meanwhile, firefighters continue to battle around the clock against the flames.
The Russian emergencies ministry said on Sunday that some 550 wildfires are currently raging, covering an area of over 190,000 hectares.
It said about 270 of those have started over the past 24 hours.