AFP-- Doctors at the government-run Vallabhbhai Patel Chest Institute say patient numbers have more than tripled since pollution levels spiked amid a change in weather conditions and the annual post-harvest burning of crop stubble in surrounding areas.

Shopkeeper Manoj Khati said he initially dismissed his heaving cough but it grew gradually worse and he has now been diagnosed with chronic bronchitis.

"For three days I haven't stopped coughing, I felt as though I would die," the 46-year-old told AFP as he waited to undergo further tests.

Levels of PM2.5 -- the fine pollution particles linked to higher rates of chronic bronchitis, lung cancer and heart disease -- regularly topped 500 this week, at one point going over 1,000

Levels between 301 and 500 are classified as "hazardous", while anything over 500 is beyond the official index.

The World Health Organization's guidelines say 25 is the maximum level of PM2.5 anyone can safely be exposed to over a 24-hour period.

Emergency ward doctor Mansi Verma said the hospital had seen a huge spike in patients suffering from respiratory problems.

They are treated with steam inhalation or using nebuliser machines, which provide immediate relief by administering drugs directly to the airways.

"Beginning this week, we are seeing between 250-300 patients, more than three times the usual," Verma told AFP.

"Most of them suffer from intense coughing and inflammation of the respiratory tract."