Thurday night was the coldest so far in Delhi this season with mercury dipping to 4.2° degrees Celsius, about 4° degrees Celsius less than the previous night, the Met department said.

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There was little respite from the biting cold on Friday as a dense envelope of fog continued to affect air, rail and road traffic in the capital.

No flights took off or landed for over six hours at the Indira Gandhi International airport in the morning.

Runway Visibility Range dropped to less than 150 metres at around 0400 IST, airport sources said.

Northern Railway cancelled some trains and reschechuled several others. The cancelled trains included the Kalindi Express, Lal Quila Express, Jammu Tawi-Delhi Express, Delhi-Jaipur Express and the Satyagrah Express.

Road traffic crawled as poor visibility caused problems for motorists.