In response, City Hall has appealed to residents to stay indoors. “The recommendations are addressed to all citizens, especially pregnant women, families with small children, the elderly and the sick.” Additionally, the use of fireplaces has been temporarily outlawed.

Worst affected are the districts of Śródmieście, Ursynów, Włochy and Wawer, though throughout the city people have been advised to keep their windows closed and avoid using transport where possible.

The situation has been blamed on the huge number of coal-fired stoves operating in Poland, the use of which has surged as temperatures have plummeted. The problem has been exacerbated yet further by a lack of wind which has allowed for the build-up of harmful particles.