The documents also reveal the government wants to build a new hospital instead of renovating Calvary Public Hospital, raising questions about the future of the privately-run hospital.

But the 10 years it would take to design and build the hospital would leave about three to four years where the ACT would be short of the beds required to service the region.

The details were revealed in government briefing documents obtained under freedom of information.

Current ACT Health planning shows by 2026-27 ACT's public hospital system would need an extra 45 adult acute inpatient beds over and above what is currently planned.

By 2031-32 this is estimated to increase to an additional 160 adult acute inpatient beds and 25 Emergency Department treatment bays.

By 2036-37, current demand indicates a requirement for an estimated additional 275 adult acute inpatient bed and approximately 55 ED treatment bays.

"Therefore, it is imperative that work on a new northside hospital continues," the briefing document said.

"Failure to plan now for the additional capacity required at 2026-27 and beyond will likely result in significant pressures on the public hospital system."

The government had previously said it favoured renovating Calvary Public Hospital over building a whole new hospital.

However the documents said it would probably be too expensive to renovate the site due to the age and deteriorating conditions of the buildings.

It brings into question the future of Calvary Public Hospital in the ACT, which is privately managed by Little Company of Mary.

Building a new hospital would require detailed "legal and contractual examination" due to its impact on the current agreement with Calvary, the documents said.

The government says it may require "sensitive negotiations".

The government is still considering whether to build the new hospital on the current Calvary site, or to build it at a new north Canberra location.

ACT Health did not directly answer questions about what would happen to Calvary Public Hospital if a new hospital was built.

"Calvary has a long history in the ACT of providing public hospital care for Canberrans and we will continue to work with Calvary on northside hospital options," a spokesman said.

ACT Health was asked how the territory would manage demand when it is scheduled to exceed capacity in 2027, even taking into account planned infrastructure work.

"This new hospital is only one part of the government's approach to managing health system capacity," the spokesman said.

"It will be complemented by other infrastructure projects, as well as both new and improved services, that will lessen demand on our hospitals and bring care closer to people, including a new $21 million elective surgery centre on the northside, expansion of Hospital in the Home, and more walk-in centres across the territory with expanded service offerings.

"Treating people who don't need to be in hospital in a more appropriate setting will improve their health outcomes and free up hospital capacity while we continue invest in new hospital infrastructure."

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A Calvary spokesman said the organisation was proud of its history of providing public hospital care for Canberrans for more than 40 years.

"There are ongoing conversations and work between the ACT government and Calvary on the future of north-side public hospital options," he said.

"We look forward to the ongoing positive relationship with the government."