India's capital city of Delhi has virtually shut down as air pollution hit "severe plus" levels, according to Indian government officials in its pollution control authority.

In several areas of the city, pollution levels were more than 50 times higher than the World Health Organization’s recommended safe limit. Forecasts say the poor air quality will continue into the week.

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.

India, Delhi’s air quality index (AQI) on Tuesday morning stood at 492, which is worse than Monday’s 483. Monday’s 483 AQI was the season’s worst but Tuesday has plummeted further.

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.

Delhi ’s government imposed the most stringent set of restrictions on the movement of vehicles and people as the toxic smog enveloping the Indian capital worsened on Monday. The city’s average air quality index was 457 in the morning,

India said on Sunday that it would tighten restrictions including on construction activities and vehicle movements in New Delhi and surrounding areas from Monday to combat worsening air quality.