A new community mental health ward will make up some of at least 120 beds added to one of Sydney's busiest hospital if Labor wins the next state election.

Canterbury Hospital would be expanded and upgraded with $225 million over the next three years, Labor said on Monday.

The hospital serving the city's south and southwest has no renal dialysis and maternity beds are shared four-bed wards that are no longer considered sound clinical practice, the opposition says.

"This is a hospital that desperately needs an upgrade. In the middle of winter patients were being treated in tents," Opposition Leader Chris Minns said in a statement.

"I'm determined to begin to meet the challenge with a comprehensive policy response, that's not only about boosting staff numbers, but delivering the health infrastructure to go with it."

The package will deliver at least 120 more beds, including in general medical, surgical, intensive care, and maternity wards.

Outpatient services will include the full suite of cardiovascular services, diabetes management, endocrinology, respiratory and cardiology, Labor says.

A new maternity ward will also be built as well as a 20-bed community mental health ward.

Funding will be drawn from the unallocated $3 billion WestInvest Government agencies fund.

Local member Sophie Cotsis said she was proud her party would redevelop the hospital for the first time in 25 years.

"Anyone who has been to Canterbury Hospital knows it is long overdue for this upgrade and expansion," the Labor MP said.