Internal documents reveal surgeons last year warned the Health Minister parts of the project would already be at capacity by the time it opens.

The expansion, dubbed SPIRE, was announced weeks before the 2016 election when the government said it would be completed by 2022.

But it has since been dogged by delays and concerns about a lack of consultation. It is now due to be completed by 2024, with construction not set to begin until 2021.

Internal notes, made in September after meetings with senior clinicians about SPIRE plans, showed a number of doctors did not believe the government had included enough operating theatres.

Dr Andrew Mitchell, ACT Health territory-wide surgical services director, warned the hospital would be at capacity as soon as the expansion was complete, the documents released under freedom of information said.

The notes said he completed his own modelling to show this, and was planning on meeting with Health Minister Rachel Stephen-Smith to discuss the theatre shortfall.

Another surgeon, Dr Wendell Neilson, said the data the government had used to base its theatre numbers on was incorrect for his specialty.

"The feeling was that 22 operating theatres was not enough, with suggestions that our facility covers (or will cover) a population of 1.5 million," an email from a SPIRE project director said.

The meeting notes showed some surgeons said they had not been consulted about the number of operating theatres needed.

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There were also concerns raised about the number of helipads to be included in SPIRE.

Currently, only one is planned, however members of a clinical advisory group strongly believe there needs to be two.

The project is slated to increase the number of theatres at Canberra Hospital from 12 to 22.

Asked whether doctors still had concerns about the number of planned theatres, a spokeswoman said the government was not aware of any current concerns.

"The ACT government is engaging regularly with clinicians and other medical professionals to ensure the new facility is fit-for-purpose and meets the needs of the growing Canberra community," she said.

"The number of theatres and patient spaces contained within the new facility will provide significantly improved patient outcomes."

The spokeswoman said more than 120 clinicians are currently involved in the project, with models of care continuing to be developed.

"The ACT government is committed to ensuring a wide range of views are considered as the Canberra Hospital expansion progresses and we will continue to listen to all interested parties to ensure the Canberra Hospital expansion meets the needs of Canberrans for years to come," she said.

Australian Medical Association ACT president Antonio Di Dio said many surgeons who were members of the association were concerned SPIRE would not have enough operating theatres.

"The key with the SPIRE project is its capacity," he said.

"When it does get finished we'll need to have enough capacity to cope with rapid increases in the territory population."

But he said while the number of theatres and beds was important, so was the government's commitment to staffing them adequately.

Dr Di Dio said the association was concerned about multiple delays to the project and wanted it "to just get done".

Opposition Health spokeswoman Vicki Dunne said the expansion had never been a priority for the government.

"Canberrans have been left with the worst performing health system after almost a decade of broken promises by Labor to upgrade failing hospital infrastructure," she said.

"Now it's looking increasingly likely Canberrans will have to wait even longer for a facility that will not meet their needs."