India, Feb. 3 -- Dense fog enveloped the national capital for nearly nine hours on Tuesday, with visibility dropping to as low as 50 metres in parts of the city, disrupting flight operations at Delhi's Indira Gandhi International (IGI) airport, where more than 200 flights were delayed between midnight and 9am, data showed.

While the lowest visibility recorded at Safdarjung was 50 metres, it stood at 100 metres at Palam. "Visibility began dipping rapidly on Monday night itself and by 11.30pm, had already touched 100 metres. It remained in this range till 8.30am on Tuesday," an India Meteorological Department (IMD) official said.

The IMD classifies fog as shallow if visibility is between 1,000 and 500 metres; moderate if between 500 and 2...