Delhi’s air quality plunged further on Thursday as dense smog enveloped the city, reducing visibility across several areas and pushing the overall Air Quality Index (AQI) to a ‘severe’ level of 428 at 8 a.m.

Several areas reported even higher pollution levels, with Anand Vihar recording an AQI of 470, Ashok Vihar at 469, and Rohini at 451, according to the Central Pollution Control Board (CPCB).

However, operations at New Delhi’s international airport were not affected by the smog, which weather officials expect to scatter during the day as breezes pick up.

Visibility remained at 300 m (980 ft), the airport operator, Delhi International Airport Limited (DIAL) said, while some airlines warned flights could be affected.

The minimum temperature in Delhi fell to 16.1 degrees Celsius (61°F) on Thursday from 17 degrees C the previous day, weather officials said.

Pollution in Delhi is likely to stay in the ‘severe’ category on Friday as well, the earth sciences ministry said, worsening to ‘very poor’ later, or an index score in the range of 300 to 400.

The number of farm fires to clear fields of paddy stubble in preparation for the planting of wheat in north India has risen steadily this week to almost 2,300 on Wednesday from 1,200 on Monday, the ministry’s website showed.

In Pakistan, Lahore, the capital of the eastern province of Punjab, was rated the world’s most polluted city on Thursday, in live rankings kept by Swiss group IQAir. Authorities there have also battled hazardous air this month.

The province has already shut schools, halted some building work, banned most outdoor activity, and ordered early closures of some businesses in efforts to combat the problem.

(With inputs from Reuters)