The Delhi airport resumed functioning on Monday afternoon after dense fog in the morning forced it to halt its operations for nearly four hours. Many flights are running behind schedule, ANI reported.

More than 300 flights were delayed and at least eight cancelled, while 400 trains reached their destinations late on account of fog, NDTV reported.

The Skymet Weather Service said most of the northwestern plains were enveloped by thick fog and the day temperature would fall significantly.

The temperature dipped to 8 degrees Celsius in the morning, and the quality of air improved. At 12 pm, the air quality in Delhi was at the “very poor” level with a reading of 385 on the Air Quality Index, the Central Pollution Control Board said. At 8 am, the AQI was 390.

The Air Quality Index at the United States Embassy in Delhi’s diplomatic enclave improved from a hazardous 482 at 8 am to 260 at 11 am, which is considered “very unhealthy”.