More than two-thirds of people believe Sydney is full and property development should be pushed to the fringes, new polling shows, amid simmering tensions within communities and the Berejiklian government over the issue.

With plans for hundreds of thousands of apartments in the city's "priority precincts" over the next 20 years, the ReachTel poll conducted for Fairfax Media shows 66.4 per cent of NSW residents oppose more development in existing areas to accommodate a bigger population.

It finds 22.8 per cent support more development in existing areas because Sydney is growing and 10.7 per cent are undecided.

Significantly for the Coalition government, 61.7 per cent of Liberal supporters believe Sydney is full, 28 per cent are in favour of more development and 10.4 per cent are undecided.