Primary schools in Delhi will shift to online classes until further directions because of rising pollution levels, Chief Minister Atishi announced on Thursday.

She made the announcement on a day when air quality in the National Capital Region plummeted to the “severe” category for the first time this winter.

On Friday morning, pollution in Delhi remained in the “severe” category at 420, according to the Ministry of Earth Sciences’ System of Air Quality and Weather Forecasting And Research, or SAFAR. At these levels, healthy people can experience respiratory illnesses from prolonged exposure to air pollution.

Visuals by ANI on Friday morning showed the area around Kartavya Path engulfed in a thick layer of smog.

On Thursday, the authorities in Delhi banned construction activities and restricted the movement of non-electric buses, as Stage 3 of the Graded Response Action Plan, or GRAP, came into force across the National Capital Region.

The GRAP is a set of incremental anti-pollution measures that are triggered to prevent the further worsening of air quality once it reaches a certain threshold in the National Capital Region region.

Apart from the restrictions on construction and non-electric buses, the authorities have also been directed to impose strict restrictions on the movement of Bharat Stage-III petrol vehicles and Bharat Stage-IV diesel vehicles that do not conform to updated emissions norms.

Residents have been urged to use public transport, work from home if possible and walk or cycle for short distances instead of using vehicles.