Delhi will consider restricting private vehicles to driving on alternate days from next week if severe air pollution continues to plague the national capital, its environment minister told Reuters on Thursday.

As choking smog enveloped the city of 20 million people this month, the state government initiated a clutch of measures such as shutting down schools, banning construction and garbage burning, allowing people to work from home, and launching various dust-control steps such as using fire trucks to spray water.

"If air pollution levels stay high, we will look at new measures like the odd-even (vehicle) system," Gopal Rai, Delhi's Minister for Environment, Forest and Wildlife Development, said in the interview.

Under the odd-even system, private vehicles can be driven only on alternating days, depending on the last digit of their number plate.

"We'll see if there's a need for a complete lockdown to tackle pollution. But these measures will not work if Delhi's neighbouring cities do not reciprocate," Mr Rai said.

More children are in hospital with breathing problems due to dangerously heavy smog in New Delhi, doctors warned on Wednesday, and the government shut five power stations and extended school closures to try to contain the crisis.

Citing a new study by the Centre for Science and Environment research body, Rai said only 30% of pollutants in Delhi's air stem from the city itself, with the rest coming from the vast urban sprawl around it where tens of thousands of big and small industries operate.

"Even if we take more measures in Delhi, air quality will not improve if our neighbouring states do not ensure that pollution levels come down in the cities that surround Delhi."

Rai said the federal government should call a meeting of Delhi and the state governments of neighbouring Punjab, Haryana and Uttar Pradesh to prepare "a joint action plan" to deal with air pollution.

"Once the joint action plan is ready, there should be an independent panel to monitor the progress on the ground."

Neither the Bharatiya Janata Party, nor the main opposition Congress is in power in the capital, giving them little incentive to cooperate with the city government run by the Aam Aadmi Party (AAP).