Transport for NSW has updated its 2016 plans following site investigations and community consultation, making multiple changes in the central section of the 15-kilometre road link.

The extension, which has been planned for more than 15 years, is proposed to divert from the motorway at Black Hill and link with the Pacific Highway at Raymond Terrace, allowing motorists to bypass the congestion points of Hexham and Heatherbrae.

Under the revised plans, there will be improved and direct access to the Hunter Region Botanic Gardens from the Pacific Highway.

An entry ramp has been moved south to allow northbound motorists out of Newcastle to join the road earlier.

Changes have also been made to the interchange at Old Punt Road to "improve connectivity, road transport efficiency and safety", and "minimise impact with the proposed AGL Power Plant infrastructure project".

"Transport for NSW has carried out additional investigations to identify necessary improvements," the agency 's revised design document says.

"This work included ... considering potential staging and examining other nearby potential projects. We have also carried out additional consultation with key stakeholders ... and have listened to previous feedback about various elements of the proposed concept design."

The motorway extension runs through the far corners of the Wallsend and Port Stephens state electorates.

Port Stephens MP Kate Washington raised no concerns about the updated designs on Wednesday, saying she was "hopeful that the Tomago interchange will unlock the jobs-rich potential in our industrial precincts, improve connectivity to the Newcastle Airport and support our tourist industry".

However, she said the NSW government needed to prioritise the project.

"This is an incredibly complex project and it's critical to our region's growth, but our community's waited long enough for the design to be finalised," she said.

"We deserve to know when construction will commence.

"It's time the M1's missing link was built."

Construction of the $2 billion motorway extension is unlikely to commence for at least another three years.

The NSW government has previously committed $200 million under its Rebuilding NSW program to get the project ready for construction.

It had spent $33 million on planning before the release of the 2019-20 budget, which included an additional allocation of $5.99 million.

Transport for NSW plans to release an Environmental Impact Statement next year.

The Morisson government committed $1.6 billion to the project in early 2019, an amount expected to fund about 80 per cent of its cost.

However, budget papers later showed the majority of the money would not be spent until the mid-2020s.

The Hunter Business Chamber, National Roads and Motorists' Association and regional advocacy body Committee for the Hunter have all previously called for planning to be fast-tracked.

Infrastructure Australia has listed the project as a priority initiative that should be delivered within the next five years since 2016.

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