The NSW government has committed to building the first stage of the F6 motorway extension from Arncliffe in Sydney's south to Kogarah but shelved the most controversial section that would have required 60 hectares of the Royal National Park or bulldozing 460 homes.

The first section of the toll road will comprise a four-kilometre tunnel of two lanes in each direction from the WestConnex motorway at Arncliffe to President Avenue at Kogarah. It will result in the acquisition of five homes in and around President Avenue, and the demolition of five others owned by the state which are tenanted.

The government was short on specifics about the design, cost and tolling for the first stage, which it said would be released in the middle of next year. However, much of the detail about the likely shape of the toll road has been released over the past six months in scores of government documents leaked to Fairfax Media.

In committing to the project on Tuesday, Roads Minister Melinda Pavey said the government wanted tunnel excavation and other construction work for the first stage to begin in early 2019.