Stage three of New Hope Group's New Acland open cut coalmine, in northwest Toowoomba, was on Tuesday given the green light by the Department of Environment and Science.

Landholders and environmentalists have protested against the project, and last year unsuccessfully tried to have it blocked in the Land Court.

The project will lift New Acland's output from 4.8 million tonnes to 7.8 million tonnes a year, and extend the mine's life for 12 years to 2034.

"The EA (environmental approval) only takes effect upon the grant of a mining tenure, which is yet to be provided," a DES official said.

"It includes a number of strict conditions, including ensuring that air and noise emissions from proposed activities are managed and monitored effectively.

"Should there be any activity prior to all approvals being granted, the independent regulator will monitor compliance with environmental obligations in accordance with the EA."

The New Acland Mine is a thermal coalmine,which provides fuel for power plants in Australia and overseas.

New Hope Group exhausted its last reserves at the mine in late November, and has made almost 300 workers redundant since 2019.

Oakey Coal Action Alliance and Lock the Gate Alliance have doggedly opposed New Acland's expansion, saying it will impact local farmers and the environment.

Meanwhile, Queensland's Liberal National Party leader David Crisafulli has criticised the glacial approval process, and last month called for the government to make a decision about the mine.

Mr Crisafulli has not revealed whether or not he supports New Acland's expansion.

However, LNP backbencher and local MP Trevor Watts signed a letter to Premier Annastacia Palaszczuk in 2021 asking for the project to be approved.

That letter was also countersigned by eight other state LNP MPs and 10 of their federal counterparts.

Australian Associated Press