The ACT government has signed the key construction and design contract with developer Multiplex to complete the project.

The Canberra Hospital expansion, originally dubbed "SPIRE", was a major election commitment in 2016 when the Labor government pledged it would be open by 2022.

ACT Health Minister Rachel Stephen-Smith said it was an "important milestone" for the project, now due to be completed at the end of 2024.

Some early work has already started at the Garran site including the completion of a new administration building and a building for the sexual health centre and staff training facilities.

"The increased capacity the fit for purpose facilities that this project delivers, will help transform emergency and critical health care for Canberrans," Ms Stephen-Smith said.

The $600 million project will feature 72 new emergency department treatment spaces, bringing the total number in the hospital to 147.

Plans revealed it will also include a new "welcome hall".

A new carpark at the former Woden CIT site, with 1100 spaces, is set to be completed by August.

Ms Stephen-Smith said the emergency department and peri-operative areas had been planned to "really improve that patient flow and patient experience through the hospital to ensure that everything is gelling and working together in the way that it should be".

"Having the state-of-the-art facility where patients flow through more easily, where the whole physical design is set up to support those models of care will be really important," Ms Stephen-Smith said.

"The emergency surgical and critical care building forms the centrepiece for the ACT government's commitment to growing Canberra's healthcare capacity."

Developer Multiplex won the contract, but Major Projects Canberra is overseeing the project.

Major Projects Canberra chief projects officer Duncan Edgehill said detailed design work still needed to be done for parts of the project and would be worked through with input from clinicians.

Prototypes of parts of the new facility including in-patient rooms will be made for staff to get a sense of how they will operate.

"It gives us an opportunity to both ensure that we're getting the design absolutely right before the main facility itself is built and also gives us an opportunity for clinicians to train in the new rooms ahead of the critical services building itself opening," Mr Edgehill said.

Mr Edgehill said demolition was the next stage in the development.

"The next step in the process on the campus itself is to demolish existing buildings," he said.

"Buildings five and 24 will then be excavated, and then the Canberra community will see the new facility level by level coming out of ground."

Ms Stephen-Smith was confident Multiplex would deliver the project on time.

Construction on the new buildings is due to begin in the coming months.

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