New Delhi -India's capital is currently covered in thick and toxic smog, which is why the authorities have now taken drastic measures.

The reason for the current high levels of air pollution in northern India is the burning of crop residues on agricultural land.

In combination with the low temperatures, the smoke remains in the air. This is driven further into the cities, where car exhausts only add to the poor air quality.

Visibility in the city of 33 million inhabitants is so poor that airlines are already warning of flight delays, according to ABC News.

Meanwhile, the level of pollution is said to be 50 times higher than the World Health Organization's recommended safety level. However, the air quality is expected to deteriorate even further in the coming days.

Today, Monday, the authorities implemented stage 4 of an action plan that includes stricter restrictions.

Schools have been closed and classes have been sent online. Trucks are no longer allowed to enter the metropolis, apart from those delivering essential items, and construction work within the city has also been halted.

Children, the elderly and people with chronic illnesses and respiratory problems have been asked to avoid being outdoors as much as possible.

The authorities have already tried to get the smog problem under control in the past with isolated measures such as water sprinklers or anti-smog guns. However, experts are pushing for more far-reaching and longer-term measures.