Delhi on Sunday woke up to a foggy morning with the minimum temperature recorded at 6.4 degrees Celsius, a notch below the season's average, the weather office said.
Meanwhile, the pollution levels crossed the hazardous mark in the national capital, with a thick blanket of smog engulfing several areas.
At least 15 trains were cancelled, 57 delayed and 18 rescheduled due to fog in several parts of northern India.
Dense fog also crippled flight operations at Delhi airport this morning with the airport completely shutting operations for over two hours leading to delays and diversions. Passengers traveling throughout the day should expect delays and cancellations due to the first day of the fog this season.
Airport sources said that the airport had to be shut for over two hours starting 7:30 leading to about 12 diversions and delays.
The humidity at 8.30 a.m. was 97 per cent and visibility stood at 400 metres.
"The sky would remain clear in the day ahead," an official of the India Meteorological Department said.
The maximum temperature is likely to hover around 22 and minimum at 6 degrees Celsius.
Saturday's minimum temperature recorded at 7.2 degrees Celsius while the maximum temperature settled at 22.6 degrees Celsius, two notches above the season's average.
According to Indian Meteorological Department (IMD), the fog condition today is expected to remain dense and continue till tomorrow.