India's top court on Wednesday accused the new Hindu nationalist government of failing to move on its promise to clean up the sewage-ridden, sacred river Ganges.

The Supreme Court urged Prime Minister Narendra Modi's government to deliver a road map on its highly-publicised pledge to restore the Ganges, which is revered by Hindus and is believed to cleanse sins.

"You are showing no urgency to protect Ganga. Are you saving the holy river?" Justice TS Thakur asked the government's top legal adviser.

"This is a part of your manifesto. What is the government doing about it?

"You are showing no urgency in this matter, only in other matters. Issues that ought to be on the backburner are out on the frontburner," he added.

Solicitor General Ranjit Kumar had appeared in the New Delhi court to seek an adjournment of the case lodged by petitioners seeking a halt to the discharge of waste into the river.

Instead the judge ordered the government to return to court in two weeks with a status report on its promise.

Deeply religious Modi offered prayers by the Ganges to underline his Hindu nationalist roots a day after his landslide election victory in May.

Modi also announced the "Ganga Mission" and appointed a minister charged with cleaning up the 2,500-kilometre (1,553-mile) long waterway, which has long been hit by untreated sewage and industrial waste.

Successive governments have attempted with limited success to restore the Ganges, which snakes across northern India from the Himalayas to the Bay of Bengal. The waterway attracts flocks of tourists and devout pilgrims who come to bathe.