Shares of Jet Airways India headed for their lowest level in almost four years after the income tax authorities conducted a "survey" at its offices, the latest trouble for an airline that has been struggling to pare losses.

"The company is fully cooperating with the authorities and responding to the queries," the airline, part-owned by Abu Dhabi's Etihad Airways, said in a filing yesterday. It said the officials have been examining its books since Sept 19 and did not provide further details.

The stock fell as much as 7.6 per cent in Mumbai yesterday, the biggest intraday loss since Aug 10.

The decline was compounded by an incident on Thursday, when pilots flying one of its aircraft forgot to maintain cabin pressure during ascent, causing injuries to many passengers.

Mumbai-based Jet Airways, which last month reported its biggest quarterly loss since 2015, is seeking to raise funds and reduce debt as part of a turnaround plan.

The carrier is among those finding it tough to make money in the Indian market, where competition has driven fares below cost.

It has said salary payments to pilots will be staggered over two instalments each month for three months.

Once among the leaders in India - the world's fastest-growing aviation market - Jet Airways has now lost shares to a slew of budget carriers like IndiGo and SpiceJet.

India's Registrar of Companies, which is under the Ministry of Corporate Affairs, has also started an initial inquiry into potential wrongdoings at the airline, such as diversion of cash, people familiar with the matter said last month. Jet Airways then said it was not aware of any probe initiated by the government.

BLOOMBERG