Toxic smog engulfed much of northern India on Monday and pollution readings in New Delhi hit their highest of this pre-winter season, after dense fog overnight.

A thick, toxic smog has enveloped India's capital, home to more than 33 million people. One technology firm which monitors air pollution ranked New Delhi as the most polluted city in the world.

New Delhi has become the most polluted city in the world after its air quality turns ‘hazardous’ at 1,081 and the concentration of PM2.5 - particulate matter measuring 2.5 microns or less in diameter that can be carried into lungs,

Delhi's air-quality index, or AQI, shot up past 1,000 on Monday, more than five times higher than Sarajevo, the second most-polluted major city.

Pollution in New Delhi shot up to its worst level of the year so far, prompting local authorities to enact emergency measures, including school shutdowns and a ban on construction work.

India's capital New Delhi switched schools to online classes Monday until further notice as worsening toxic smog surged past 60 times the World Health Organization's recommended daily maximum.- 'Stay indoors' - Primary schools were ordered to cease in-person classes on Thursday,

India's capital New Delhi switched schools to online classes Monday until further notice because of worsening toxic smog, the latest bid to ease the sprawling megacity's health crisis.