Delhi woke up shrouded in fog on Wednesday morning, with little visibility and 'very poor' air.

The India Meteorological Department (IMD) issued an orange alert for dense fog between 8.30 am and 10 am.

Visibility was recorded at 50 metres at both Palam and Safdarjung at 6.30 am, the weather office said. The national capital recorded a 24-hour average Air Quality Index (AQI) of 384, according to data from the Central Pollution Control Board (CPCB).

A station-wise breakdown showed that 21 monitoring stations recorded 'very poor' air quality, while 16 stations were in the 'severe' category, with Anand Vihar registering the worst AQI at 452, according to data from the CPCB's SAMEER app.

According to CPCB classification, an AQI between 0 and 50 is considered 'good', 51 to 100 'satisfactory', 101 to 200 'moderate', 201 to 300 'poor', 301 to 400 'very poor', and 401 to 500 'severe'.

The air quality outlook remains grim, the Air Quality Early Warning System said, with the AQI likely to deteriorate to the 'severe' category on January 1, before letting up to the 'very poor' category on January 2.

For the subsequent six days, air quality is expected to remain 'very poor', it said.

Officials attributed the poor air to an unfavourable ventilation index of below 6,000 square metres per second and average wind speeds of less than 10 kmph, which are not conducive to the dispersion of pollutants.

At least 118 flights were cancelled, 16 flights diverted and 130 services delayed at the Delhi airport on Tuesday as dense fog disrupted operations.

The Indira Gandhi International Airport (IGIA), operated by DIAL, handles around 1,300 flights daily. An official said 60 arrivals and 58 departures were cancelled while 16 flights were diverted at the airport. Information from flight tracking website Flightradar24.com showed that 130 flights were delayed on Tuesday morning at the airport and the average delay time for departures was around 28 minutes.