Authorities in the India capital, Delhi, have shut all schools and colleges indefinitely amid the worsening levels of air pollution.

Construction work has also been banned until 21 November but an exception has been made for transport and defence-related projects.

And only five of the 11 coal-based power plants in the city have been allowed to operate.

A toxic haze has smothered Delhi since the festival of Diwali.

The levels of PM2.5 - tiny particles that can clog people's lungs - in Delhi are far higher than the World Health Organization's (WHO) safety guidelines. Several parts of the city recorded figures close to or higher than 400 on Tuesday, which is categorised as "severe".

A figure between zero and 50 is considered "good", and between 51 and 100 is "satisfactory", according to the the air quality index or AQI.

A mix of factors like vehicular and industrial emissions, dust, and weather patterns make Delhi the world's most polluted capital. The air turns especially toxic in the winter months as farmers in neighbouring states burn crop stubble. And fireworks during the festival of Diwali, which happens at the same time, only worsen the air quality. Low wind speed also plays a part as it traps the pollutants in the lower atmosphere.

This year, the pollution has become so dire that it prompted a stern warning from India's Supreme Court, which directed state and federal governments to take "imminent and emergency" measures to tackle the problem.

Following the hearing, a meeting was called by Delhi's Commission for Air Quality Management and emergency measures were announced.

Other measures announced by the panel include a ban on the entry of trucks in Delhi and neighbouring states of Uttar Pradesh, Punjab, Haryana and Rajasthan until 21 November, except those carrying essential commodities.

The panel also directed Delhi and other states to "encourage'' work from home for 50% in all private offices that fall in the National Capital Region during the period.