A blanket of toxic air continued to blanket New Delhi and the National Capital Region on Friday as the air quality index breached emergency levels. A public health emergency was declared in the afternoon, and construction activities were banned till November 5. Schools will also remain closed till then.

The index read 468 at 10 am, according to the Central Pollution Control Board, hours after breaching the “severe plus” mark late on Thursday night, Hindustan Times reported. It was the first time since January that air quality dipped to emergency levels in the national capital. The pollution control board calculates a 24-hour average. Air this bad falls in the severe category, and “affects healthy people and seriously impacts those with existing diseases”. The Centre-run System of Air Quality and Weather Forecasting and Research, or SAFAR, recorded a severe-plus reading of 533 at 10.50 am.

Chief Minister Arvind Kejriwal again blamed crop burning in neighbouring states for the increase in pollution. “Delhi has turned into a gas chamber due to smoke from crop burning in neighbouring states,” he tweeted. “It is very important that we protect ourselves from this toxic air. Through private and government schools, we have started distributing 50 lakh masks today. I urge all Delhiites to use them whenever needed.”

On Wednesday, Punjab Chief Minister Amarinder Singh had criticised Kejriwal for blaming his government for the rising pollution in the national Capital. He claimed Kejriwal was trying to “divert public attention from his own government’s failures” by indulging in such “outright lies”.

The Central Pollution Control Board has asked Punjab and Haryana to take immediate action to curb stubble burning.