Hunter Westpac rescue helicopter machine .

Mega spend ... the cost of building the helicopter base has blown out from $30 million to $50 million. Photo: Supplied

A NEW helicopter base larger than seven football fields and costing $50 million would be built in Parramatta under NSW government plans.

The new ''mega base'' designed for rescue services would be built on the site of the old Parramatta City Raceway site near the M4, which is now called Sydney Speedway, said Ian Badham, an executive director of the rescue helicopter service CareFlight.

Mr Badham has been told by bureaucrats that the estimated cost of building the helicopter base on the speedway had blown out from about $30 million to $50 million.

Mr Badham was also told that the Health Minister, Jillian Skinner, put the project on hold near the end of last year to await the findings of a comprehensive review of the state's rescue helicopter services, which was released this week.

The recommendations include reducing the number of rescue helicopters in NSW from 15 to 12 to save money.

If built as currently planned, Parramatta's new helicopter base would have four hangars, 720 square metres of office space, overnight accommodation and ''underwater training capability'', the report by the consultants Ernst & Young reveals.

Plans to build on the site are ''well progressed'', said a senior industry source who spoke on the condition of anonymity.

A spokesman for Mrs Skinner said: ''I think it would be incorrect to say plans are well under way … The option of building a helicopter base at Parramatta was deferred until the review was complete so that all stakeholder submissions are considered. There are several other options.''

But plans for the helicopter base are far enough along for them to be included on Ambulance Services NSW's forward capital works, Ernst & Young said.

Ambulance Services NSW declined to respond.

Asked whether he had heard of the government's plans to build a helicopter base on his company's racetrack, a Sydney Speedway spokesman said: ''I've spoken to my managers and the answer is no comment.''

A $50 million helicopter base would be a significant infrastructure investment for the City of Parramatta, but the lord mayor, John Chedid, said he knew nothing about it.

''To be honest I'm shocked … It's the first I've heard about it,'' Cr Chedid said.

''It's very significant and it's something we would welcome to Parramatta. I think it's a worthwhile investment and something critical for the area of emergency.''

Most Parramatta residents ''will be very understanding'' about the potential noise of helicopters as the project would help to expand the city, Cr Chedid said.

The lord mayor believes the speedway, which is located off James Ruse Drive and the M4, is the most logical place to put a helicopter base as it is a large parcel of land far enough away from residents.

But he reiterated that he was shocked that he had not heard about the plans, as the speedway site had been a central part of Parramatta since the 1970s.

The speedway has hosted many national titles over the years, including the Australian Sprintcar Championship, the Australian Speedcar Championship, the Australian Super Sedan Championship and the global sprint car series ''World of Outlaws''.

The NSW Ministry of Health and Ambulance Services NSW have prepared a ''preliminary business case'' for the new rescue helicopter base.

A Parramatta base would replace the existing facilities at Bankstown Airport, which the Ernst & Young report describes as inadequate.

''The Bankstown base has … congested air space and traffic procedures which adversely impact on response times,'' the report says.

''We understand that a confirmed delivery date for the new Sydney base has yet to be established and is unlikely to be before 2015-16.''