Minister for Regional Transport and Roads Paul Toole said two separate packages for design and environmental reporting work were on offer to professional services firms with experience in providing world-class infrastructure.

"The NSW Government is investing $2.5 billion in the Great Western Highway upgrade, which will improve congestion and provide safer, more efficient and reliable journeys for all road users travelling in, around and through the Blue Mountains," Mr Toole said.

"The project is moving ahead with Registrations of Interest now open for pre-qualified contractors to design and prepare environmental assessments for the eastern section of the upgrade from Katoomba to Blackheath, excluding Medlow Bath, and the western section from Little Hartley to Lithgow."

Mr Toole said that it was a complex project that needs to work around steep land and they want to minimise the impacts on the environment and preserve the heritage and character of the communities affected.

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"By working on assessments for these two sections at the same time, this will allow us to deliver benefits sooner to everyone who uses the highway, as well as providing an investment and employment to boost the NSW economy," he said.

"The project is expected to create about 2,500 jobs during the peak construction period."

Mr Toole said the design of the two sections was a significant step for the project and proposals would go through a detailed selection process to shortlist tenders for either the east or western section.

Firms will not be permitted to tender for both sections.

Transport for NSW plans to award the tenders later in 2020.