The NSW government's plans to deliver thousands of new homes on Sydney's northern beaches have been heavily criticised by the state's transport department, which has refused to support the project until further assurances are made.

In December, the NSW government unveiled its plan to transform 700 hectares of land in Ingleside, near Mona Vale, into a new community comprising 3400 new homes for as many as 9000 residents, while conserving large parcels of bushland.

According to the Department of Planning's draft strategy, the timing of the development will be "co-ordinated with the increased capacity to be provided by Mona Vale Road upgrades," which will involve the road corridor being expanded to two lanes in each direction.

But in a submission to the government's draft strategy, Transport for NSW attacked the assumption as inaccurate, noting there was "no forward budget for these proposed upgrades".