Air traffic at the Delhi airport came to a standstill for almost 12 hours since Sunday night as thick fog engulfed the Capital. The drop in runway visibility to 100 metre at 9 pm on Sunday forced suspension of flight operations up to 9.13 am on Monday, when a Lufthansa jet landed.

Most domestic flights were delayed 3-4 hours on Monday. "Though we expect the backlog to be cleared, the problems will multiply if the fog thickens," an airline executive said.

Officials at the Delhi airport said they were in constant touch with the meteorological department. Extra ground staff had been put on duty, more seats added in the lounges and supplies at restaurant and coffee bars had been enhanced, they said.

Indian Airlines executives said the airline was trying to limit diversions to nearby airports like Ahmedabad, Lucknow and Jaipur. On Sunday night, 13 domestic flights were diverted to Jaipur, Indore and Ahmedabad. Seven international flights were diverted to Mumbai. Four international flights were diverted to Mumbai on Monday.

Most international airlines, such as British Airways, Singapore Airlines, Cathay Pacific and Sri Lankan Airlines, have revised their schedules to avoid the fogs. The revised schedules are being followed since last week.

Domestic airlines are combining certain flights. Jet Airways has combined its Chennai and Lucknow flights, while Indian Airlines combined its Ahmedabad and Vadodara flights.

The first domestic departure, of an Indian Airlines flight to Chennai, was at 9.39 am on Monday. Runway visibility reached 1,400 metres at 1 pm. On Sunday, Indian Airlines cancelled its Ahmedabad and Chennai flights, while Jet cancelled its Leh, Bhopal, Chandigarh and Varanasi operations.