Western Sydney's ageing and under-resourced public hospitals will be upgraded in a $3 billion budget blitz announced by the NSW government.

Four hospitals will receive a total $3 billion in funding for major infrastructure improvements as part of commitments announced by Premier Chris Minns on Sunday.

Some $400 million will be set aside to build the $700 million Rouse Hill Hospital, the first new hospital for the western corridor in 40 years.

The facility will include an emergency department, maternity services, ambulatory and outpatient care and medical imaging services.

Fairfield, Canterbury, Bankstown-Lidcombe, Blacktown and Mt Druitt hospitals are part of the state government's "game changer" capital investment package that aims to increase capacity and ease pressure on health services in the harbour city.

Fairfield Hospital will receive its first refurbishment since opening 34 years ago, while Canterbury Hospital will be redeveloped for the first time since 1998.

More than $1 billion has been committed to building a new site for the Bankstown-Lidcombe Hospital, which merged from two facilities in 1997.

The commitments form part of a push for 600 new beds across Sydney's stretched western health services.

"When you look at the recent statistics over the last few years, we need to do better when it comes to the number of beds and the services provided by the hard-working men and women in NSW Health," Mr Minns told reporters.

He said funding allocation for hospital upgrades has come at the expense of infrastructure projects not backed by return on investment, with information on those to be released when the budget is handed down on September 19.

A 70 per cent return in salary sacrifice for health workers has also been agreed between the government and union representatives.

While other jurisdictions in Australia offer 100 per cent returns, Mr Minns said this is an important step in returning equity and fairness back to the system for NSW health workers.

"As a result of this decision, they know there's more money in their pocket," he said.