New Delhi/IBNS: The Delhi-National Capital Region (NCR) experienced the worst Air Quality Index (AQI) on Monday morning as the toxic smog engulfed the union territory causing more worries for the residents, media reports said.

The AQI plummeted to the 'severe-plus' category reducing the visibility to 150 metres at 5 am.

The AQI recorded 481 at 7 am. 

The flight and train services have been affected by the air quality, which has tumbled due to pollution at the onset of the winter season.

The Stage-4 of the anti-pollution plan GRAP was implemented by the Centre at 8 am.

Under the Stage 4 of GRAP, no trucks barring the ones using clean fuel or the ones carrying essential items will be allowed inside the national capital.

Light commercial vehicles carrying non-essential items will be barred from entering Delhi.

Barring the ones carrying essential items, BS-IV vehicles or the ones using older fuels will be barred in the national capital.

Delhi Chief Minister Atishi has announced all school classes will be held online except for students of Classes 10 and 12.

The Chief Minister wrote on X, "With the imposition of GRAP-4 from tmrw, physical classes shall be discontinued for all students, apart from Class 10 and 12. All schools will hold online classes, until further orders."

All kinds of construction works will remain suspended.

The Supreme Court will on Monday resume hearing on the case pertaining to air pollution.

Last week during a hearing, Amicus curiae and senior advocate Aparajita Singh told the top court bench comprising Justice Abhay S Oka and Augustine George Masih that Delhi should not become the most polluted city in the world.

"We are in severe mode today. They (Delhi government) have not yet taken any pre-emptive measure yet. Nothing has been done. We should not become the most polluted city in the world," advocate Singh told the top court as quoted by Bar and Bench.