The proposal is part of a suite of reforms announced by the NSW Government in a bid to encourage the private sector to absorb some of the demand on the overcrowded public school system, which is expected to accommodate a further 170,000 students over the next 15 years.

Announcing the reforms in February, Education Minister Rob Stokes said the policy package would streamline the planning approval process and "make it easier to deliver well-designed, high-quality schools where they are required".

At least 15 councils across Sydney have raised objections to the reforms. Their criticism centres on key measures that will allow private schools to build millions of dollars worth of new buildings either without development approval from councils, or through a fast-track pathway of "complying development".

Under the reforms, both public and private schools will be allowed to build four-storey structures, as high as 22 metres, through the process of complying development, which does not require a development application and is instead approved by an accredited certifier.

The reform is designed to fast-track the larger-scale educational buildings, including classrooms, administration buildings, gyms, and sporting facilities, which are already permitted as complying development but are restricted to a 12-metre height limit.

The new measures would also enable schools to develop childcare facilities on their grounds.

Councils strongly objected to the height increase for areas where schools have views of the ocean or Sydney Harbour because complying development does not require a merit assessment of a building's visual impact.

Mosman Council, which has three schools located inside a designated "scenic protection area" taking in foreshore slopes of Sydney and Middle harbours, said the measure posed a "considerable risk to the natural and visual environment" of the area.

Under another measure, private schools will be permitted to operate as "public authorities", allowing them to build one-storey buildings without requiring development consent from councils.

The City of Sydney and Woollahra councils, whose local districts are home to some of the state's most elite private schools, have condemned the policy as creating a system where private schools function as both developers and assessors of their own infrastructure.

While this process is already used by the Department of Education for public schools, the City of Sydney slammed the move as "setting a dangerous precedent of allowing private entities to operate outside the planning system with no protection for the public interest".

Sydney, in its submission on the proposed reforms, said the changes would not create a "level playing field" because public schools "are bound to act in the public interest" and were accountable through the government of the day, whereas private schools "act in the interest of their fee-paying students".

Woollahra Council, which has 15 private schools within its small district including the prestigious Cranbrook School, Ascham School and The Scots College, also refused to support the reforms on the grounds they would allow private institutions "to act in conflicting roles" without adequate transparency.

"They are developer, they appoint the person to assess the development proposal and they determine the proposal. There is a lack of independence in this process," the council's submission said.

The government says the "development without consent" provisions are designed to permit only minor expansion of schools, which would be legislatively constrained to a 10 per cent expansion and require approval of the Roads and Maritime Authority for increases of 50 students or more.

"They must comply with a rigorous code of practice, meet environmental assessment requirements and engage with the community," a spokesman for the Planning Department said.

But a number of councils remained concerned that, in the absence of any requirement to assess cumulative developments, schools would use the provisions to undertake much larger expansions, potentially creating significant flow-on problems with traffic, parking and neighbouring properties.

"For example, the repeated use of the 10 per cent provision over five years for a school with a starting population of 1000 could result in an increase of over 500 places," Mosman Council submitted.