Air quality in the Indian capital Delhi has deteriorated to severe and extremely poor levels in recent days, data shows.
Last week, pollution levels exceeded 25 to 30 times the safe limit recommended by the World Health Organization (WHO) at several locations in the city.
Experts have warned that the situation will worsen in the coming days due to weather conditions, the use of firecrackers during the Diwali festival on Thursday and the burning of leftover crops in neighboring states.
Delhi and several cities in northern India report extreme levels of air pollution between October and January each year, causing disruptions to businesses and the closure of schools and offices.
Levels of tiny particles (known as PM 2.5), which can penetrate deep into the lungs and cause many illnesses, reached 350 micrograms per cubic meter in some areas on Monday, according to data from government website Safar . .
According to the website, air quality is classified as very poor when PM 2.5 levels reach 300 to 400, and it is classified as severe when the limit reaches 400 to 500.
Delhi is shrouded in a thick layer of smog every winter due to smoke, dust, low wind speed, vehicle emissions and stubble burning.
In November and December, farmers in the neighboring states of Punjab and Haryana burn stubble to clear their fields.
Farm groups say they need financial and technical help to find other ways to clean up leftover crops, but government programs have so far not been effective.
Smoke from firecrackers set off during Diwali adds to the problem.
Like every year, the Delhi government has announced a complete ban on the manufacturing, storage and sale of fireworks ahead of the festival, which falls later this week.
But such bans haven't been completely effective in the past because people source their fireworks from other states.
The Delhi government has also adopted its Phased Response Action Plan, known as GRAP, to tackle pollution.
It prohibits all activities involving the use of coal and firewood, as well as the use of diesel generators for non-emergency services.
Delhi authorities have warned residents to stay home as much as possible and curbed construction activities in the city.
They also urged people to use public transport to reduce vehicle emissions.
