Amid worsening pollution levels in Delhi, the Centre's air quality panel on Saturday directed authorities in the National Capital Region to immediately implement curbs under stage III of the Graded Response Action Plan (GRAP).

The restrictions include a ban on construction and demolition activities except for essential projects concerning national security, defence, railways and metro rail among others.

The Commission for Air Quality Management (CAQM) also said that the authorities might impose restrictions on the plying of BS III petrol and BS IV diesel four-wheelers in the NCR considering the worsening air quality.

Delhi's 24-hour average air quality index stood at 397 at 4 pm, the worst since January. It was 354 on Thursday, 271 on Wednesday, 302 on Tuesday and 312 on Monday (Diwali).

GRAP is a set of anti-air pollution measures followed in the capital and its vicinity according to the severity of the situation.

It classifies the air quality in the Delhi-NCR under four different stages: Stage I - 'Poor' (AQI 201-300); Stage II - 'Very Poor' (AQI 301-400); Stage III - 'Severe' (AQI 401-450); and Stage IV - 'Severe Plus' (AQI >450).

Under stage III, the authorities have been asked to enforce a strict ban on construction and demolition activities in the NCR, except for essential projects (such as railways, metro, airports, ISBTs, national security/defence-related projects of national importance) and non-polluting activities such as plumbing, carpentry, interior decoration and electrical works.

Brick kilns, hot mix plants and stone crushers not operating on clean fuels, and mining and associated activities in the NCR have also been banned.

State governments in the Delhi-NCR may also impose restrictions on BS III petrol and BS IV diesel four-wheelers under stage III, the CAQM said.