New Delhi, Jan 7 (TIWN / IANS) At least 13 trains and several flights headed towards the national capital were delayed due to fog as the visibility dipped to zero metres on Monday morning.

According to the India Meteorological Department (IMD), the visibility dropped to zero metres for Palam between 6.30 a.m. and 7.30 a.m. while it was 200 metres for Safdarjung.

"Fog Alert - Low Visibility Procedures have been implemented at Delhi Airport... Passengers are requested to contact the airline concerned for the updated flight info," the official Twitter handle of the Indira Gandhi International Airport stated.

Runway Visibility Range of upto 50 metres is required for an aircraft to land, it said.

Jet Airways also announced, "due to adverse weather conditions (fog) at Delhi... some of our flights have been affected".

The visibility improved at 8.30 a.m. to 50 metres.

The minimum temperature was recorded at 7.1 degrees Celsius, the season's average, with the rainfall at 8.30 a.m. recorded at 1.6 mm. The humidity level was 100 per cent.

"The city will witness moderate fog throughout the day," an IMD official said.

The overall air quality of the city was recorded in the 'very poor' category with Air Quality Index (AQI) recorded at 340, according to the System of Air Quality and Weather Forecasting And Research (SAFAR).

On Sunday, the minimum temperature was recorded at 8.6 degrees Celsius, a notch above the season's average, while the maximum settled at 19.6 degrees Celsius, the season's average.