On the Skopje streets, numerous citizens were wearing masks in a bid to protect themselves while the visibility was poor.
Mask stocks were emptied, local media reported.
According to a World Heath Organisation (WHO) study, published in early 2017, Skopje, which is located at the bottom of a valley, was among ten cities in Europe with the highest concentration of fine particles.
Last winter, the situation was critical for two weeks.
On Friday, the quantity of fine particles was 500 micrograms per cubic metre of air or ten times higher then recommended by the WHO.
Due to the pollution and fog, the authorities limited air traffic since Thursday afternoon, without numerous flights being cancelled or diverted.
Skopje's Social Democratic mayor Petro Silegov called the citizens to "change their habits, walk or use public transport."
On Facebook some parents said that they had decided "being fully aware" not to send their children to school until the air will be cleaner.
"The citizens are demanded not to breed until spring," a Skopje resident commented ironically.
"What ideas do you have for cleaner air in Macedonia?" the US embassy in Macedonia asked on Twitter.
"As our friends from US embassy are searching for ideas for the air pollution in Macedonia we want to help with a solution. Turkish Stream," replied the Russian embassy, referring to a gas pipeline through Turkey that would enable Balkan countries to get Russian gas.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)