New Delhi. New Delhi has just got over the worst bout of smog in years but, after an interlude of clear weather, thick fog has now descended on the Indian capital and nearby regions, hitting road, rail and air travel.

Visibility fell to below 50 meters early on Thursday (01/12), forcing Indira Gandhi International Airport to suspend operations and, according to reports, causing at least four domestic flights to be diverted.

"There was dense fog during the night which caused a lot of problems. It is natural and can lead to accidents on the road," said passenger Ravinder Singh, who had come from Punjab state and was flying to Sydney via Bangkok.

"By God's grace, my flight is on time right now," he said, looking at a flight information board.

Fifty trains were running late, the Northern Railways said, while poor visibility in other cities like Amritsar also disrupted road traffic. Weather forecasters said the fog was expected to persist for another six days.

North India, and in particular New Delhi, suffers from a temperature inversion at this time of year that traps air pollution.

With fog settling, air quality readings deteriorated and the U.S. Embassy's monitoring station recorded an air quality index (AQI) of 297 that is classified as "very unhealthy".

Still that was not as bad as readings that approached 1,000 - literally off the AQI scale that runs to 500 - during a recent "airpocalypse" caused by firecrackers during the Diwali festival and burning of crop stubble by farmers in nearby regions.

Reuters