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.

An Air-India flight from Mumbai, scheduled to arrive at 2.15 am, and a Thai Airways flight from Bangkok had a delayed landing.

?We informed our head office at night that no flight could land because of fog,? said a spokesperson for Thai Airlines. The flight finally landed in the city at 12.20 pm and took off at 1.30 pm, hours after its scheduled departure at 1.45 am.

A Royal Jordanian Airlines flight to Amman was to leave at 11 pm on Saturday. The take-off was deferred to Sunday morning. An Air Deccan flight to Delhi at night was also stuck and left at 8 am on Sunday.

The first take-off on Sunday morning, of a Port Blair-bound Alliance Air flight, was at 6.45 am. It was scheduled to leave at 5.35 am.

Among the flights delayed were of Indian Airlines, headed for Delhi and Mumbai.

As for the disruption on the tracks, two long-distance trains arrived late at Howrah station, Eastern Railway officials said.

The Jamalpur-Howrah Express arrived one-and-a-half hours late, while the Dibrugarh Town-Howrah Kamrup Express was three hours behind schedule.