The bench posted the matter for hearing on September 4.

The National Highways Authority of India (NHAI) told the Supreme Court on Thursday that the Rs 10,000 crore Salem-Chennai 8-lane green corridor road project is of "national importance" and the Madras High Court had erred in quashing the land acquisition process.

The ambitious 277.3-km greenfield project connecting Salem and Chennai under the central government's Bharatmala Pariyojana scheme aims to cut travel time between the two cities by half, to about two hours and 15 minutes.

The NHAI told a bench headed by Justice N V Ramana that the high court had held that environmental clearance (EC) was mandatory for the project.

"The reasons given by the high court (in the judgement) are factually incorrect," Solicitor General Tushar Mehta, appearing for the NHAI, told the bench which also comprised Justices M M Shantanagoudar and Ajay Rastogi.

Mr Mehta said the high court erred in saying that grant of prior environmental clearance was necessary for the project.

"If we have to take environmental clearance first and then go for land acquisition then it will be like putting the cart before the horse," Mr Mehta told the bench.

He said there was no dispute on the fact that EC is required before commencement of construction work for the project.

One of the advocates, appearing for the farmers who had moved the high court challenging land acquisition proceedings, told the bench that initially the project was for connecting Chennai and Madurai but later it was changed to Salem-Chennai.

The bench told Mr Mehta that he should give a flow chart referring to legal questions as well as the factual matrix of the case.

"Two points will be important. One is environmental clearance and other is change of route from Chennai-Madurai to Chennai-Salem," the bench observed, adding, "Ultimately, we will decide the law".

"The high court has also given a finding that this (Chennai-Salem project) is not a part of the Bharatmala project. You have to answer this also," the bench told Mr Mehta.

The bench posted the matter for hearing on September 4.

At the end of hearing, Mr Mehta told the court that "this is a project of national importance".

The National Highways Authority of India has moved the top court against the high court's verdict which had come on a batch of petitions filed by 35 land owners and PMK leader Anbumani Ramadoss.

In its verdict, the high court had made it clear that grant of prior environmental clearance would undoubtedly require a thorough study of the area and before that, a public hearing was needed to be conducted.

The ambitious project has been facing opposition from a section of locals, including farmers, over fears of losing their land, besides environmentalists who are against felling trees for it.

"We are of the considered view that the project highway as conceived and sought to be implemented is vitiated on several grounds... and consequently, the notifications issued for acquisition of lands under Section 3A(1) (of the National Highways Act) are liable to be quashed," the high court had said.

Environmental clearance was mandatory since the project would have an adverse impact on the environment, including water bodies, the high court had said.

If the project highway was to pass through reserve forest area, even if it is to a distance of about 10 km, it would undoubtedly pave the way for poachers and facilitate easy access, the high court had said, adding it would also pave way for illicit felling and transportation of valuable timber.