NEW DELHI, Dec. 15 (Xinhua) -- Hundreds of flights were cancelled or delayed Monday as thick smog blanketed the Indian capital territory and its outskirts, officials said.

Local newspaper The New Indian Express said due to poor visibility, Indigo has announced the cancellation of 109 flights, while Air India has cancelled 37 flights. Air India Express has announced that 20 flights have been impacted across its network in Northern India.

Another newspaper Hindustan Times said 400 flights were delayed due to low visibility as a thick blanket of smog covered the capital regions.

Meanwhile, Delhi's average Air Quality Index (AQI) settled at 498, firmly within the higher end of the severe category.

The Delhi government has urged residents, especially children and those with respiratory or cardiac ailments, to stay indoors and use masks if going out.

Industrial activities and traffic are significant contributors to air pollution in the city, along with rampant construction. Air pollution continues to worsen during the winter months. ■