New mothers with mental illness from around NSW will be able to keep their newborns with them while they get the care they need.

The first public mother and baby mental health unit in NSW opened on Wednesday at Sydney's Royal Prince Alfred Hospital.

The Naamuru ('leading the way') unit has eight beds available to provide care for up to 120 mothers and their babies every year.

The bedrooms are large enough for a mother, two babies and another family member.

A second unit will open at Westmead later this year.

Mothers with acute mental illness will be referred to the Naamuru unit from all around the state.

Premier Dominic Perrottet said mental health was a challenging area of the healthcare sector, particularly for new mothers.

"Dealing with issues of depression at the time they've just given birth to their child, and to be separated at birth, that would be incredibly difficult to be going through," he said.

Keeping mothers with their babies while they are treated could make a real difference, he said.

Jen Whitlam stayed at a private hospital for six weeks with postnatal psychosis following the birth of her son Arlo.

"I had never experienced a mental health issue in my life before," Ms Whitlam said.

"For a large part of that hospitalisation I was separated from Arlo because there was no such public facility that was able to provide a space that was safe for Arlo to be with me."

The new public unit will help expand the private care she was able to receive for new mothers facing similar challenges.

"I hope that this unit is able to create the space, the support and the confidence (for women) to be able to move forward as a healthy and happy family," Ms Whitlam said.

Women, Mental Health and Regional Health Minister Bronnie Taylor said the unit would provide the right care at the right time.

"It's been designed with people with lived experience, people that have been through these issues themselves and come through the other side," she said.

Ms Taylor hopes similar units will open in regional areas "very soon".

"What we can do well we will absolutely do locally ... I want to see that access right across the state," she said.

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