Building a new panel cave plus plant expansion has already created 100 jobs in the planning stages and will lead to "hundreds more jobs" in the construction stages.

Orange will benefit from increased demand for housing for the staff and flow-on effects for retail shops.

A further $185 million expansion is also planned for approval next year.

Orange mayor Reg Kidd said he was "thrilled" the work would start soon.

"This project will see several hundred jobs created which will see available roles for local male and female contractors," he said.

"The project will have a huge flow on effect into the town's economy."

Orange Business Chamber president Ash Brown said real estate agents were already getting rental enquiries from prospective workers. He said it would lead to rental and house price rises.

Mr Brown said it was "the icing on the cake" following other announcements including new industry at the old Electrolux site and construction of the Bloomfield medical complex.

He said it could rival the Cadia-led economic boom of several years ago.

A major international, national and local recruitment campaign will seek a range of workers for the mine.

The expansion will involve the development of a new mine area, Panel Cave 2-3, materials handling system upgrades, associated infrastructure and initial works to increase the plant capacity.

The expansion plan has improved on a pre-feasibility study announced last year and is expected to add 1.8 million ounces of gold output and 67,000 tonnes of copper, with an $800 million increase in projected free cash flow generation by Cadia over the life of the mine.

Newcrest Managing Director and Chief Executive Officer Sandeep Biswas said it was a significant boost.

"The capital investment has an estimated 21.5 per cent rate of return and ensures Cadia remains a Tier One asset for many years," he said.

Cadia Valley Operations general manager Peter Sharpe said it was "great news for Cadia and for the region".

"Recruitment for more workers to support the project is underway, with [about] 100 new positions for early works filled to date," Mr Sharpe said.

Mr Sharpe said "hundreds more" workers would be needed for the construction phase.

"The estimated capital cost of stage one of the project is $685 million, with a further $185 million expected for stage two which will be submitted for approval around the middle of 2020."

The mine will also boost water saving efficiency measures which a Cadia statement said had resulted in net water recycling rates increasing from about 65-70 per cent to about 85 per cent.

He said external water use had been cut by 30 per cent in the past 18 months.

Construction of the 98,000 square metre panel cave 1400 metres below the surface is set to start this year.

It is expected to start production in 2023.

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