Air pollution chokes New Delhi every winter, but this year's smog has already derailed everything from transport and road work to schools.

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.

Around 38% of the pollution in New Delhi this year has been caused by stubble burning - a practice where stubble left after harvesting rice is burnt to clear fields - in the neighbouring states of Punjab and Haryana, according to SAFAR, a weather forecasting agency under the ministry of earth sciences.