Delhi saw cold wave conditions for the fifth consecutive day on Monday as very dense fog reduced visibility to just 25 metres, hitting road, rail and air traffic movement, officials said.

The cold wave spell in Delhi has been so intense that the national capital has recorded a minimum temperature lower than that of most places in Himachal Pradesh and Uttarakhand for five days on the trot.

Meteorologists attribute the long spell of intense cold to a large gap between two western disturbances, which meant frosty winds from the snow-clad mountains blew in for a longer-than-usual period.

The visibility levels dropped to 25 metres at the Palam observatory, near the IGI Airport, and the Safdarjung observatory, Delhi's primary weather station, an official of the India Meteorological Department (IMD) said.

Around 29 trains have been delayed by two to five hours due to the foggy weather, a railway official said.

Around 15 flights were delayed and one was diverted due to the bad weather, officials at the Indira Gandhi International Airport said.

Satellite images showed a fog layer extending from Punjab and adjoining northwest Rajasthan to Bihar through Haryana, Delhi and Uttar Pradesh.

The minimum temperatures in the national rose marginally though. The Safdarjung observatory recorded a minimum of 3.8 degrees Celsius as against 1.9 degrees on Sunday.

The weather stations at Lodhi Road, Ayanagar and Ridge recorded a minimum temperature of 3.6 degrees, 3.2 degrees and 3.3 degrees.

The Safdarjung observatory had logged a minimum temperature of 1.9 degrees Celsius on Sunday, 2.2 degrees Celsius on Saturday, 4 degrees Celsius on Friday, 3 degrees Celsius on Thursday and 4.4 degrees Celsius on Wednesday.

It (Monday) was the fifth consecutive day that Delhi's minimum temperature was lower than most hill stations in Himachal Pradesh and Uttarakhand, including Chamba (8.7 degrees), Dalhousie (9 degrees), Dharamshala (9.2 degrees), Shimla (10.3 degrees), Manali (6 degrees), Kangra (8.9 degrees), Dehradun (6.5 degrees), Mussoorie (11.3 degrees), Nainital (6 degrees), Mukteshwar (7.6 degrees) and Tehri (9.2 degrees), according to the IMD.

The chilly weather has prompted the Delhi government to extend winter vacation in schools till January 15.

"The long cold wave spell in Delhi can be attributed to a large gap between two western disturbances which allowed the chilly northwesterly winds from the mountains to affect the plains for a longer-than-usual period," Mahesh Palawat, vice president (meteorology and climate change), Skymet Weather, said.

Usually, there is a gap of three to four days between two western disturbances. This time, the gap increased to seven days, Palawat said. A western disturbance retreated from the region by December 30 and the next one came on January 7.

A senior IMD meteorologist said short-term relief is likely after a couple of days under the influence of back-to-back western disturbances.

When a Western disturbance -- a weather system characterised by warm moist winds from the Middle East -- approaches a region, the wind direction changes. Hence, the chilly northwesterly winds from the mountains will stop blowing for a few days leading to an increase in temperatures, he said.

The IMD said the foggy weather may lead to road accidents and advised people to drive slowly and use fog lights.

It said there are chances of tripping of power lines in areas witnessing very dense fog.

Long exposure to dense fog may cause respiratory problems for people having asthma bronchitis and other lung-related health problems, it said.