Air India has cancelled 85 budget flights following a mass sick leave strike. [AFP]

Air India's budget carrier subsidiary cancelled 85 flights on Thursday, a day after its operations were severely disrupted by dozens of cabin crew calling in sick at the last minute.

The airline was taken over by Indian conglomerate Tata Group in 2022 after a government effort to privatise the heavily indebted carrier.

Media reports linked the sudden mass sick leave to simmering staff discontent over new policies on hiring and promotion imposed by its new ownership.

Air India Express said in a statement that it had made "every possible effort to minimise the inconvenience caused to our guests" but had been forced to cancel 85 flights on Thursday.

"We urge our guests booked to fly with us to check if their flight is affected by the disruption before heading to the airport," it added.

More than 90 other flights had been "disrupted" since Tuesday by the resulting staff shortages, the airline said in a separate statement on Wednesday, without clarifying whether they had been delayed or cancelled.

Chief executive Aloke Singh said Wednesday that the airline had been forced to curtail its flight schedules over the coming days.

"Since last evening, over 100 of our cabin crew colleagues have reported sick before their rostered flight duty, at the last minute, severely disrupting our operations," Singh said.

"This act is certainly not representative of the 2,000-odd cabin crew colleagues in the company who continue to respond to the call of duty."

Media reports said the budget carrier had sacked at least 20 staff.

An Air India Express spokesperson said Thursday that the airline taken "appropriate steps against certain individuals", but did not provide further details.

"We are taking appropriate steps against certain individuals as their actions have caused grave inconvenience to thousands of our guests," the spokesperson said.

New Delhi airport saw chaotic scenes on Wednesday as agitated passengers waited for updates on delayed and cancelled flights, according to Indian media reports.