NEW DELHI, Jan. 1 (Xinhua) -- Flights and train services were severely affected in the Indian capital on Monday as a blanket of dense fog enveloped the city for the second day in a row, officials said.

"At least 12 flights have been hit in the morning. Five domestic and seven international flights to and from Delhi's Indira Gandhi international airport have been delayed, while one flight has been cancelled," an aviation official said.

The runway visibility at the airport had dropped below 50 metres, he added.

Similarly, nearly 90 trains to and from the two main railway stations -- New Delhi railway station and Old Delhi railway station -- were affected by dense fog.

"Some 56 trains have been delayed, 20 rescheduled and 15 cancelled due to dense fog in and around the Indian capital. Several passengers have been stranded at the railway stations," an official of Northern Railways said.

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

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