A thick blanket of fog over the city threw flight and train operations haywire between late Saturday and early Sunday.
Several international and domestic flights could not land or take off.
A number of flights were diverted to other destinations, while a few were rescheduled.
"The visibility level was below 100 metres at one point of time and it was not possible for any flight to operate," said an official at Netaji Subhas Chandra Bose International Airport.
Flights were grounded after 9.30 pm on Saturday, as the runway was enveloped by fog. Four domestic and two international flights were diverted and the arrival of two other flights were rescheduled, civil aviation officials said.
According to airport officials, a Jet Airways flight on the Pune-Mumbai-Calcutta route was diverted to Nagpur, while another on the Bangalore-Hyderabad-Calcutta route was diverted to Hyderabad.
A Sahara Airlines flight from Mumbai was diverted to Hyderabad and a SpiceJet flight had to return to Hyderabad, officials said.
A Singapore Airlines flight, scheduled to arrive at 10.35 pm, was diverted to Bangkok. A British Airways flight from London, which was to arrive at 1.30 am, was diverted to Dhaka. Both flights arrived on Sunday.
