A bench headed by Chairperson Swatanter Kumar directed each state to submit details about two most-polluted cities in their territories, including data on pollution from dust, vehicular density and population. The matter will next come up for hearing on July 11-12.

The directions came after the counsel for the automobile industry pleaded before the tribunal not to pass orders before hearing auto makers' contentions.

Industry body Society of Indian Automobile Manufacturers ( SIAM ) said vehicles with diesel engines displacing 2 litre and more are not a major cause of pollution. The contribution of these vehicles is minuscule, unlike dust which is the major source of pollution in the country, its counsel argued.

The central government, too, had moved the NGT saying any ban on diesel vehicles would hurt investments and employment in the manufacturing sector.

Additional Solicitor General Pinky Anand,representing the Centre, said about 8% foreign direct investment under 'Make in India' has come from the auto industry and that the sector generates large employment opportunities.

"We don't want the industry to suffer, which is why the government has brought fuel guidelines. The whole idea is that people must prosper. The tribunal passed an order but the same was stayed by the high court. There aren't enough evidences to show that diesel vehicles are causing more pollution," Anand said after the hearing.

The NGT had recently banned the sale of large diesel-powered passenger vehicles in some cities of Kerala, but that order was stayed by the state high court.

In the National Capital Region, however, registration of large diesel cars and utility vehicles isn't happening since December because of a ban imposed by the Supreme Court.

Anand said there must be broad long-, short- and medium-term plans to curb pollution.

The National Green Tribunal is hearing a petition that seeks to put restrictions on diesel-powered vehicles to reduce air pollution in 11cities, including the metros of Mumbai, Hyderabad, Chennai, Kolkata and Bengaluru.

Overall, industry experts say, about 4 lakh diesel vehicles with 2-litre or larger engines are sold in the country annually.

The ban in the NCR has already resulted in a production loss of 11,000 vehicles, affecting 5,500 jobs, including at dealerships, according to the Society of Indian Automobile Manufacturers. Had the ban been countrywide, it would have led to a loss of 47,000 jobs, it estimates.

The local units of Toyota and Mercedes-Benz, and Mahindra & Mahindra are expected to be hit the most if the ban is extended to more areas, as several of their popular vehicles come under the banned category.