Project managers Parsons Brinckerhoff and Korean construction company Posco, which is also touted as an investor in the final project, were told late last week to stop work on the Carmichael mine, rail and port project.

Company sources said senior Adani executives flew to India at the weekend for talks about the project's future.

It comes less than a month after Adani stood down four engineering firms – WorleyParsons, Aecon, Aurecon and SMC – and scores of workers involved in preparatory works on the development, which would open up Queensland's vast Galilee Basin.

"It seems to me like they're at the crossroads of do they continue or do they do what GVK did and sack everyone," one source said.

"I think they just don't have the money and can't get the money to go ahead. I think, one, Adani don't have the money, and two are realising this is a long, drawn-out process."

It also follows revelations by Fairfax Media that senior Queensland Treasury officials had advised the Queensland government last year that they believed the project was unviable.

Adani insisted on Tuesday that the mine would still go ahead and it was not pulling out of Australia.

"These structural changes are connected to the same engineering contracts and preliminary works variations Adani announced last month," an Adani spokeswoman said.

Parsons Brinckerhoff referred requests for comment to Adani, while calls to Posco were not returned.

Adani staff were told last month that the engineering firms were suspended while it waited for approvals from the Queensland and federal governments that are required before work can begin.

Parsons Brinckerhoff are the principal project management consultant on the project, while Posco had been set to build Adani's 388-kilometre rail line from the mine to Abbot Point and take a financial stake in the development.

The standing down of both key firms is viewed by workers involved in the development as an extraordinary step.

Queensland's Labor government included no potential royalties from the project in its recent budget. But it has continued to back the development despite calls for an inquiry after hundreds of pages of confidential Treasury correspondence raised serious concerns about Adani's transparency and its ability to finance the coal mine.

During the Queensland election campaign Labor pledged that it would not invest in a rail line connecting Adani's mine to coal terminals at Abbot Point.

But Fairfax Media reported last month that Queensland's Department of State Development had prepared a briefing for ministers on alternative options for assisting Adani, including a so-called "royalty holiday" period that would save the company hundreds of millions of dollars if its mine goes ahead.