New Delhi: As dense fog enveloped several parts of the national capital Thursday, 55 trains were cancelled and 25 remained partially cancelled across northern railways, officials said.

At least 12 trains were delayed due to low visibility, they said.

Some prominent trains including Puri-New Delhi Purushottam Express, Howrah-New Delhi Poorva Express, Bhagalpur-Anand Vihar Garib Rath Express, Varanasi-New Delhi Kashi Vishwanath Express and New Jalpaiguri-New Delhi Express have been delayed by several hours, the railways said.

Most of the affected trains were running late by two-three hours due to very low visibility around the national capital, they said.

The situation, however, was much better this year because of 'Fog Pass', a safety device that was provided to railway zones worst affected by fog, they added.

A Global Positioning System (GPS) based handheld, portable device, the Fog Pass serves as an aid for the crew during low visibility conditions through an audio-visual alarm whenever a landmark comes within its geo-fence range.

A total of 6940 devices were provided across the railway network with 2648 in the Northern Railway alone.

According to the Indian Meteorological Department (IMD), the national capital will be engulfed by shallow fog on Friday as well.