Adani staff working on the early phases of the mine, which would open Queensland's vast Galilee Basin, were told last Thursday and Friday they were out of a job.

Adani itself is denying it has begun retrenching staff with a spokesman saying: "suggestions of a fresh decision in relation to staffing late last week are simply not true."

But multiple sources have told Fairfax Media the company intends to keep a skeleton workforce of about 20 people.

The remainder, about 90 engineers, safety officers and other mining personnel, have been told their departures will be staggered between the months of August and March.

Company sources said workers were told they were being made redundant because of delays in getting approvals for the project from the Queensland and federal governments.

"They're basically doing what GVK did – sacking everyone but keeping a few people there," one source said.

A second said Adani was reducing its workforce from "more than 100 to about 20".

Fairfax Media revealed last week that Adani had stood down two major contractors – its project manager Parsons Brinckerhoff and Korean construction company Posco, which had been touted as an investor in the final project.

The company has also suspended four engineering firms, WorleyParsons, Aurecom, Aecon and SMEC.

The dismissals have raised questions about whether Adani intends to continue with the project, which has received praise from both sides of politics.

But Adani continues to insist it is pushing ahead, and on Thursday engineering firm Downer EDI announced it had received two letters of intent from Adani for contracts on the project, including one contract that would be a joint venture with Posco.

Downer EDI's statement said the letters of award could be terminated if contracts had not been entered into by September 30.

Adani's spokesman said none of the company's Brisbane staff had been sacked.

"As indicated when asked previously, there were changes over a week ago in relation to project management and execution contracts which were connected to the same engineering contracts and preliminary works variations that Adani announced last month," Adani's spokesman said.

"The preliminary works contracts were previously sustained due to the level of investment Adani had maintained for more than 12 months in anticipation of a range of government decisions and approvals timeframes.

"As we announced on 24 June 2015, a number of changes in the approvals processes meant these timeframes had to be adjusted."

The spokesman added that "if and when there are changes to our response to approval timeframes" the company would make an announcement.

"Adani does not propose to comment on ill-informed speculation," he said.

Queensland's Labor government has continued to back the project, despite its own budget not including any potential royalties from the mine and revelations that Treasury officials had advised that they believed the development was unviable.