Temperatures in Moscow are expected to rise beyond a scorching 32 degrees Celsius (90 Fahrenheit) on Tuesday, as environmentalists warned of dangerously high levels of pollution in the city.
Monday was the hottest day this year, with a high of 31.9 degrees, the Interfax news agency reported, citing a regional weather bureau spokesman.
And the temperature is expected to climb in the coming days. Wednesday's forecast calls for 31-33 C in the city, with 35 C predicted by the weekend.
Pregnant women, people suffering from cardiovascular and respiratory diseases, and the elderly have been advised to take extra measures to protect their health after the city's environmental monitoring agency issued a pollution warning.
But this week's heat wave could have been much worse: The hottest temperature ever recorded in the city for July 29 came just four years ago, when the thermometer hit a scorching 38.2 C (100 F) at the height of a summer-long heatwave.