NEW DELHI, Jan. 4 (Xinhua) -- Dense fog enveloped the Indian capital Thursday, severely disrupting air and rail traffic in the city.

At least 20 flights to and from Delhi's Indira Gandhi International Airport and over 50 trains have been affected due to dense fog that has shrouded the city since the early hours of the day as temperatures dipped to as low 5.7 degrees Celsius, officials said.

"Some 20 domestic and international flights have been delayed to and from Delhi's Indira Gandhi International Airport owing to low runway visibility because of dense fog," a senior aviation official said.

Flight operations will resume once the fog clears up later in the day, he added.

"Similarly, some 50 trains have been delayed or rescheduled to and from the two main railway stations -- New Delhi railway station and Old Delhi railway station. However, no trains have been cancelled," a senior Indian Railway official said.

Since Sunday, several flights have been affected in Delhi due to thick fog as the runway visibility levels also dropped below 50 metres. Even train services had been hit by fog.

Fog is common in northern India, particularly in the winter months of December and January, and is responsible for many road accidents.