A thick layer of toxic cloud covers most parts of northern India today, while the air pollution in New Delhi reached a level above 60 times higher than the upper limit set by the World Health Organization (WHO), according to IQAir measurements.

The concentration of PM2.5 microparticles (the most dangerous because they diffuse directly into the blood) was measured in the morning at 907 micrograms per cubic meter of air in some parts of the metropolis of 30 million inhabitants, according to IQAir.

The PM2.5 particles are carcinogenic and enter the bloodstream through the lungs.

The city faces record levels of air pollution every winter from toxic fumes from factories and road traffic, compounded at this time of year by the seasonal burning of agricultural residues.

Cooler temperatures and light winds in winter, which lasts from mid-October to at least January in India, intensify the phenomenon.

Local authorities activated level 4 of their alert plan on Sunday afternoon “in order to avoid further deterioration of air quality”.

Most schools in the region remained closed today, traffic restrictions were tightened and workers were told to prefer to work remotely until further notice.

Schools in the capital are conducting distance learning today by decision of the authorities, with the exception of two high school classes due to worsening air pollution.

In addition to the closure of the majority of classes, other measures were taken including restrictions on construction sites and the movement of diesel trucks.

The government also urged children, the elderly and anyone with heart or lung disease to “stay indoors as much as possible”.

According to the WHO, air pollution can cause cardiovascular and respiratory diseases as well as lung cancer.

A study published last June found that air pollution is responsible for 11.5% of mortality in Delhi, or 12,000 deaths annually.

In October, India’s Supreme Court ruled that access to clean air was a fundamental right, ordering central and state governments to act.