Construction of two major motorway tunnels in Sydney’s north will be expected to start in 2022 at the earliest, which is at least a year later than what the state government has originally planned.

Transport and Roads Minister Andrew Constance also highlighted on Tuesday that the cost of the Western Harbour Tunnel and Beaches Link could be higher than estimates in 2017 of $14 billion.

"There will be a little bit of escalation but we are going to market. We have seen across the board a real challenge ... both in terms of capacity constraints [and] risk appetite among contractors," he said. "We have to go out in stages because the market can't deliver this in one go."

The toll-road project includes two 6.5 kilometre tunnels from an underground junction for the WestConnex toll road at Rozelle to the Warringah Freeway at North Sydney. The 7-kilometre Beaches Link will extend from the freeway to Balgowlah and Seaforth in the city's north-east.

"Cabinet-sensitive" plans, dated May last year, have shown construction on both roads were planned to begin from 2020-21, and be opened to motorists in 2025-26. Regardless of the original plans, Mr Constance said that "ideally we will start to see construction in 2022", or by the time of the next state election in 2023.

The government's immediate focus will be realigning four kilometres of the Warringah Freeway – one of the busiest motorways in Australia – followed by the Western Harbour Tunnel, which will be built using large concrete tubes submerged in a trench.

An environmental impact statement for the Western Harbour Tunnel and freeway upgrade will be released in January, followed about six months later by one for the Beaches Link.

"The aim will be to work through the planning process over the next 12 to 18 months," Mr Constance said. "Once you have completed the project planning, and obviously the procurement, you are looking at a five-to-seven-year build. For instance, there are three projects – the Warringah Freeway, the Western Harbour Tunnel, the Beaches Link."

Labor roads spokesman John Graham said it meant there will be a longer wait than the residents of Sydney's northern beaches had expected for the promised road tunnel.

"This is another project without the funding fully tied down," he said.

Among 68 properties − 52 of which are homes – will be acquired for the motorway project. So far, 15 properties have been purchased by the state.

Balgowlah Golf Course will be adopted as a construction site for the project, and eventually returned to the community as public space with new sporting facilities. Part of the Cammeray Golf Course will also be used during construction.

Leaked documents have shown that motorists will be slugged about $8 (in today's dollars) for a one-way journey by car on the entire length of the new tunnels from Rozelle to Balgowlah.

It was also revealed by The Herald that the government has been considering tolls on both directions on the Sydney Harbour Bridge and the Harbour Tunnel to help cover the cost of the new road tunnels.

Mr Constance said the tolls would be finalised as "we work towards that final cost" of the project.

"There will be a toll [on the Western Harbour Tunnel and Beaches Link] because we have got to actually finance the infrastructure in order to build it," he said.

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