Delhi's air quality has deteriorated to "severe" levels according to authorities, which can affect healthy people and seriously impact those with existing diseases. On Wednesday, the capital's PM2.5 levels in the air reached 438, according to the Central Pollution Control Board - dangerously high concentrations of fine particles that can clog the lungs.
This is nearly 30 times higher than the World Health Organisation's safe limit and about eight times higher than India's national average. The WHO considers a 24-hour average of no more than 15 to be safe.