A new Adelaide women's hospital will be built next door to the new Royal Adelaide Hospital (RAH), which is about to open its doors in the north-west of the CBD.

South Australian Premier Jay Weatherill said the $528 million women's hospital would be physically connected to the new RAH, and was expected to be completed by the end of 2024.

"The new Adelaide women's hospital, positioned next to the new Royal Adelaide Hospital, will be a modern, purpose-built facility that will care for women and newborns for many generations," he said.

The SA Government first proposed a relocation of the Women's and Children's Hospital from North Adelaide into the city before the 2014 state election.

It said it would identify a site by the end of 2019 for a new children's hospital near the other new hospitals in what journalists put to him as a "piecemeal approach" to services currently offered under the same roof.

Mr Weatherill said the Government was acting on the "basis of the best advice we have", which was to "do it in phases".

"Clinicians said the element that's most important and should happen first is the bringing together of birthing services and the new Royal Adelaide Hospital, so if there's complications, women can get that seamless set of services," he said.

This week's SA budget will also have an additional $24 million over two years toward an overall $64.4 million upgrade of the existing Adelaide Women's and Children's Hospital.

Health Minister Jack Snelling said there were great advantages in locating the two hospitals side by side.

On the new Royal Adelaide Hospital's helipad, the Premier announced another hospital would be built next door. ( ABC News: Nick Harmsen )

"Our doctors say this model will be of great benefit, in particular in situations where a mother may experience a difficult birth and require acute intensive care at the new Royal Adelaide Hospital," he said.

"Having access to the new Royal Adelaide Hospital's helipad will also significantly improve the timeliness of access to air services for high-risk maternal and neonate emergencies."

Women to get emergency care at RAH

SA Health released a fact sheet stating the new women's hospital would continue to provide tertiary level maternity, neonatal and perinatal infant mental health services.

"By co-locating with the new Royal Adelaide Hospital women with high-risk or emergency care needs will be able to receive timely and direct access to adult intensive and sub-specialty care," it read.

It said clinicians would decide where seriously ill newborn babies would be treated.

"There will be some newborns that will need to be stabilised at the new Adelaide Women's Hospital and transferred to the Adelaide Children's Hospital for specialist paediatric care, including for example, where specialised surgery is required," it said.

"How the care models will work at both sites will be developed by expert clinicians."

SA Health said a small number of staff would be required to work across both the women's and children's hospitals.

Ahead of Thursday's state budget, the Government has also announced upgrades for Adelaide's major public hospitals — the Queen Elizabeth, Lyell McEwin, Modbury and Flinders Medical Centre.

Staff of the existing RAH are in final training ahead of the state's biggest public hospital opening at its new premises on September 5.

Opposition Leader Steven Marshall said the Liberals remained committed to a single new Women's and Children's Hospital.

He said the Labor Government had scaled back services, been plagued by project delays and "almost" abandoned its original health plans.

"The people of South Australia deserve the best health system in the country and only the Liberal Party will deliver that," Mr Marshall said.