By Tanvi Mehta NEW DELHI (Reuters) -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. Visibility dropped to 100 metres in the capital and at least eleven flights were diverted.

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.

India's capital New Delhi was wreathed in blanketing toxic smog this week as worsening air pollution surged past the grim mark of 50 times World Health Organization recommended daily maximum.

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.

In several areas, pollution levels were more than 50 times higher than the World Health Organization's recommended safe limit.

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.