“The temperature is high compared to what it is usually at this time of the year,” said director of Alipore Met department, GC Debnath. “And it will remain so for the next 72 hours,” he said, indicating that Thursday morning too, may be very foggy. Thankfully, a slight drizzle is expected in the next 24 hours in parts of South Bengal, which might make Friday clearer.

The fog began to descend on the airport and surrounding areas from 3 am on Wednesday, said Met department officials. And it lasted for nearly six hours. The visibility came down to zero, rendering the Instrument Landing System (ILS) ineffective and forcing Air India, Jet Airways, Kingfisher, Lufthansa and British Airways to reschedule flights.

The ILS system requires a minimum visibility range of 350 m. “We have been experiencing dense fog since December last year. But this is a recent phenomenon. Possibly we will think about upgrading our ILS system from CAT II,” said a ground and flight safety official. A British Airways flight to London scheduled to depart at 5.05 am was cancelled. After a wait of over two hours, the 271 passengers were taken back to their hotels and the flight was rescheduled for 1 am on Thursday morning.

An Air India flight carrying Haj pilgrims to Kolkata from Jeddah supposed to land around 4.30 am was diverted to Nagpur. A Spicejet flight to Delhi was the first flight to take off today while an Indigo Airways flight from Delhi was the first flight to land at 9.20 am.

The scene was no different at the Howrah station, which saw harried passengers waiting on platforms. Four major long-distance trains of Eastern Railway and six of South Eastern Railway were delayed for hours. “When I booked ticket online in the morning there was no information about trains running late. Now, as I reach the station, I am told that my train is delayed for four hours,” said Sumi Chakraborty (20), a Jadavpur resident, who was scheduled to board Janashatabdi Express from Howrah. Despite the presence of information centres at railway stations, passengers were seen complaining about the inadequate assistance at stations. “The railway authorities never give us the correct information. Their enquiry numbers mostly go busy. We left our hotel and came here only to find out that our train is running late for hours due to dense fog. Now we do not even know where to go,” said Dr Sanjay K Verma, who heading for Patna.