The Indian mining giant Adani has announced it will self-finance its controversial Queensland coalmine project and says major works are due to start “imminently”.

Adani has made a string of announcements in recent months that indicated the company would scale back its mine, rail and port plans plans, having been unable to find an outside investor.

The company’s Australian mining chief, Lucas Dow, said on Thursday the mine would be a “smaller open-cut mine comparable in size to many other Queensland coalmines” and that work would now begin.

“The project stacks up both environmentally and financially,” Dow said.

“Today’s announcement removes any doubt as to the project stacking up financially. We will now deliver the jobs and business opportunities we have promised for North Queensland and Central Queensland, all without requiring a cent of Australian taxpayer dollars.

“In addition to providing these jobs in regional Queensland our Carmichael coal will also provide a power source to improve living standards in developing countries.”

The Carmichael mine has become the symbolic battle front for both environmentalists and proponents of coal.

Dow made the company announcement in Mackay, while the surrounding areas of central Queensland were engulfed in a what is considered an “unprecedented” heatwave and bushfire emergency.

The Australian Conservation Foundation said the announcement meant Adani was a “step closer” to building its mine, but called on elected representatives to intervene.

“This financing announcement means ignorance, denial or avoidance are no longer viable,” the ACF chief executive, Kelly O’Shanassy, said. “The only responsible response is to stop Adani and keep Galilee Basin coal in the ground.

“The Stop Adani movement will fight this proposed mine every step of the way. There is too much at stake.”

In a statement, Adani acknowledged it still had some “remaining required management plans” to finalise “ahead of coal production” and that the process for those should be completed within weeks.

But Guardian Australia has confirmed construction cannot start until two of those regulatory hurdles are cleared. Critical rail and royalties agreements, both which add more than $100m to the cost of the project, also remain unsigned.

The Queensland Department of Environment and Science told Guardian Australia last week that “significant disturbance cannot commence at the [Carmichael] site” until two plans were approved.

One of those is a groundwater-dependent ecosystem management plan (GDEMP). The department says Adani has to “identify the [previously unknown] source of the Doongmabulla Springs” before it can approve the plan. Adani says it has done so.

The GDEMP must be approved by the Queensland government and is a requirement of Adani’s federal approval.

“DES continues to provide feedback to Adani to ensure that the GDEMP meets approval requirements,” the department said in a statement last week.

“The GDEMP also needs to be approved by the federal Department of Environment and Energy, who will seek independent scientific review from CSIRO and Geoscience Australia.

“There is no statutory timeframe for DES to assess the plans.”

Adani also requires approval for a management plan for the black-throated finch before being allowed to start work.

Adani has also not yet signed a royalties deal with the Queensland government, which analysts estimate would be worth $315m to the company in deferred payments during the early years of production. Questions remain about whether Adani can meet the terms of state government’s royalties framework that would allow such a deal.

Adani also has to negotiate access to the Aurizon rail network. It is unclear who will pay for necessary upgrades to the railway.

Julien Vincent, the executive director of Market Forces, an NGO encouraging environmentally sustainable investment, said the latest announcement was “an act of desperation from Adani”.

“[Adani] knows the window of opportunity to build its Carmichael mega coalmine is rapidly closing,” he said.

“It’s also an admission of failure, as the company has tried and failed for almost a decade to find a financial backer and now has no option but to move its unpopular project ahead with its own capital.

“Adani’s claim of financial close remains highly questionable. Financial close is what happens when everything is in place. This is a project that still doesn’t have all of its approvals.”