Residents of Delhi woke up to a thick blanket of toxic smog, prompting the city to cancel in-person classes, halt construction and limit traffic, as the Indian capital city's air-pollution levels surged past 60 times the World Health Organization's recommended daily maximum.

A thick blanket of toxic smog engulfed most parts of northern India on Monday and readings of air quality in the capital New Delhi hit their highest this year after dense fog overnight.

India's pollution control authority has classified the air in Delhi as "severe plus", after the city passed 450 according to its measurements on Monday morning.

Delhi recorded air pollution more than 17 times above an acceptable level as worsening smog triggered curbs on trucking and shuttered construction sites and schools.

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.