The Delhi government on Thursday announced the closure of all schools in the national capital till further orders because of an increase in the air pollution levels.

However, board exams will continue as scheduled and teaching-learning activities will be conducted online, it said.

The decision came hours after the Supreme Court pulled up the Delhi government for resuming physical classes in schools despite an increase in the air pollution levels in the city.

"We had reopened the schools considering the forecast that air quality would improve. However, the air pollution levels have increased again and we have decided to shut schools from Friday till further orders," Delhi Environment Minister Gopal Rai said.

Education Minister Manish Sisodia said, "All board exams will be conducted as per schedule".

After remaining shut since November 13, physical classes in schools, colleges and other educational institutions had resumed from Monday.

Citing challenges posed by the new Covid variant, Rai said the situation isn't good for running metro trains and buses at full seating capacity.

So, there has been no discussion on odd-even (car rationing scheme), he said.

The Delhi government had earlier extended the ban on the entry of trucks, barring those engaged in essential services, till December 7. CNG and electric trucks are allowed to enter Delhi.

The ban on construction and demolition activities in Delhi will also continue till further orders in view of the high air pollution levels.

In a bid to reduce vehicular pollution, the government has started a special bus service to ferry its staff from government residential colonies in 14 areas in the city and extended the 'Red Light On, Gaadi Off' campaign till December 18.

The air quality in the national capital slipped into the "severe" zone again on Thursday with the slow wind speed -- due to a western disturbance affecting northwest India -- allowing accumulation of pollutants.

The city's air quality index read 430 at 3 pm.

Mahesh Palawat, Vice President (Meteorology and Climate Change), Skymet Weather said the skies will clear up on Friday and the situation may improve slightly due to a marginal increase in the wind speed.

However, the relief will be short-lived as another western disturbance will cause the winds to slow down again from Saturday, he said.

Delhi's air quality this November was the worst for the month in seven years with the city witnessing severe pollution on 11 days and not a single day of "moderate" or "better" air quality, according to Central Pollution Control Board (CPCB) data.

Experts said though stubble burning remains a major factor behind the spike in the air pollution levels in the early phase of winter, local sources of emissions are the primary reason for highly polluted air in the city in the post-farm fire period.

According to an analysis by the Ministry of Earth Sciences' air quality forecast agency SAFAR, local sources accounted for 78 per cent of the air pollution in Delhi from November 22 to 26.