Dense toxic smog blanketed India’s national capital Monday, pushing air pollution levels to their worst levels in weeks, disrupting travel and causing authorities to impose the strictest containment measures.

Axar.az informs, citing AP, more than 40 flights were cancelled and several dozens delayed. Over 50 trains arriving and departing from New Delhi were delayed by several hours, authorities said.

Healthcare experts warned residents to avoid all outdoor activities as hospitals reported an influx of patients with breathing difficulties and eye irritation.

“New Delhi is a gas chamber right now. Air purifiers can help only a bit, so it’s high time the government comes up with some permanent solutions” said Naresh Dang, a physician at Max Healthcare.

Delhi’s air pollution levels have remained at what the federal government calls a “severe” level for the last two days, which the government says can cause respiratory effects to healthy people and seriously affect the health of people with heart or lung disease.

On Sunday, official index readings were over 450 at several monitoring stations, up from 430 on Saturday and the highest so far this winter season, as per data from Central Pollution Control Board. On Monday, it stood at 449. Readings below 50 are considered good. During periods of severe air pollution, the government advises people to avoid going outdoors as much as possible and wear N95 masks when going outside. Children, pregnant women, elderly and people with pre-existing respiratory or cardiovascular conditions are at higher risk and officials advise them to be extra cautious.

New Delhi and its surrounding region, home to more than 30 million people, routinely rank among the world’s most polluted.

India has six of the world’s 10 most polluted cities, and New Delhi is the most polluted national capital, according to a report from Switzerland-based air quality monitoring database IQAir earlier this year.

A study last year by medical journal Lancet linked long term exposure to polluted air to 1.5 million additional deaths every year in India.