Indian customs allege Adani Group siphoned 15 billion rupees or AU$290 million into overseas tax havens, but the claims were denied by the company, The Guardian has reported.

Adani is vying for a $900 million concessional loan from the Northern Australia Infrastructure Facility to build a rail line for its Galilee Basin Carmichael mine to the Abbot Point coal terminal.

An Indian Directorate of Revenue Intelligence file from 2014 alleged a money trail from India to a company in Mauritius that was controlled by Vinod Shantilal Adani, the brother of Adani Group chief executive Gautam Adani.

The allegations included that the Adani Group ordered hundreds of millions of dollars worth of equipment for an electricity project in India using a front company and sold it back to businesses it controlled at a "gross over-valuation".

If true, it would have had the effect of moving the money to overseas bank accounts where it could not be taxed.

Some of the money allegedly moved out of India was taxpayer-funded in the form of loans from a publicly-owned bank.

GetUp environmental campaign director Sam Regester said the revelations meant public money should not be given to Adani for its Carmichael mine.

"This is just way too much risk and it's a lose-lose proposition for Australian public money," he said.???

An Adani Australia spokesman told Fairfax Media the allegations involved Adani's parent company and had nothing to do with the company in Australia.

The allegations were four years old, the spokesman said, and Adani Australia had nothing to add.

Attempts were made to contact Adani in India.

Adani Group told The Guardian that on behalf of itself, its subsidiaries and Vinod Adani that it strongly denied allegations of over-valuation.

The company said it was standard procedure for the group to follow international competitive bidding routes for major capital expenditure to ensure transparency and competitiveness.

All transactions were conducted within regulatory guidelines and provisions, Adani Group told The Guardian.

"The fact that our projects have incurred the lowest cost across central, state and private utility players has gone to establish the robustness of the processes followed by our group," it said.

Adani Group said it was fully cooperating with the DRI investigation.

A spokeswoman for Queensland Premier Annastacia Palaszczuk said NAIF was a matter for the Turnbull government.

Comment was sought from Acting Resources and Northern Australia Minister Barnaby Joyce.???

NAIF was also approached for comment, but a spokeswoman said the body did not comment publicly on the specifics of proposals or the status of due diligence processes.