Smog from wildfires in the countryside cloaked Moscow on Friday, with the levels of toxic particles, raising alarm over public health and numerous commuters wearing anti-pollution masks.
The city's most famous landmarks like the spires of the Kremlin towers or the onion domes of Orthodox churches were largely invisible from a distance as Muscovites wheezed their way through the smog into work.
"Smog has covered the entire city and the situation is getting worse," said Alexei Popikov of Moscow's pollution monitoring service Mosekomonitoring on state television.
Air traffic was disturbed at one of Moscow's main international airports -- Domodedovo in the south of the city -- with planes taking off normally but some aircraft landing at airports elsewhere due to the smoke.
Mosekomonitoring said that this week that the concentration of toxic particles in the air was higher than the norm by a factor of 20 in some areas and even people in good health should consider staying at home.
Early morning commuters were wearing anti-pollution masks as pharmacists reported a huge spike in sales of the masks.
Forecasters warned that the record heatwave was going to continue in the coming days, with little rain forecast and the mercury again expected to hit 38 degrees Celsius (over 100 degrees Fahrenheit) later.
Russia is battling its worst forest fires in modern history with emergency services still struggling to contain the flames.
Explore further: Moscow wheezes as smog cloud blankets city