The Centenary Hospital was only opened in 2012, but has come under significant capacity pressure ever since.

A $50 million expansion - announced in 2017 - is currently under way and is due to be completed in the 2021-22 financial year.

But the latest figures contained in Canberra Health Services' annual report showed the hospital was now not set to be completed until September 2023.

It's yet another delay from the original expected completion of 2020-2021.

The hospital is located on the Canberra Hospital campus, but is a separate project to the $500 million SPIRE expansion of that hospital.

That expansion is also running years behind the original schedule, with construction yet to begin despite Labor in 2016 saying it would be open by 2022.

Canberra Health Services deputy chief executive Dave Peffer said designing the right hospital was more important than working towards a deadline.

He said several key changes to the scope of the Centenary expansion, including changes made from feedback from patients, had pushed the completion date out.

"These improvements include the addition of upgrades to the paediatric adolescent ward and the decision to build the new adolescent mental health unit adjacent to it," he said.

"The original plans did not include significant refurbishment of the paediatric adolescent ward, and the new adolescent mental health unit was to have been built in a separate building."

He said changes would allow specialised clinical staff to work together more effectively, which would include a sensory modulation room, parent lounge, parent overnight accommodation and an enhanced care area for vulnerable patients.

EDITORIAL: We can do better than endless hospital delays

The scope also changed to include a dedicated early pregnancy unit to support for women and their families who experienced early pregnancy loss.

"While the full expansion project will not be completed until September 2023, the first component, the refurbished paediatric high care ward, opened to patients in October 2020," Mr Peffer said.

"Expanding and upgrading a working hospital requires a staged delivery to ensure minimal impact on health services and operations.

"One benefit of this is that completed elements can be opened once ready rather than at the end of the entire project."

The hospital has faced significant building quality issues since its opening.

In 2018, 15 delivery suites and bathrooms had to be fixed due to water leaking into the wall cavities. There were also issues with the paediatric unit, part of which was closed for months due to plumbing issues.

The hospital has been prone to flooding during periods of heavy rain.

In 2017, it was discovered the hospital's cladding was potentially combustible and a process to remove it began.

The new completion date comes after it was recently revealed Canberra could run out of hospital beds as early as 2026.

The government is planning to build a new north-side hospital, however, it would not be open for at least 10 years.

It has also brought into question the future of Calvary Public Hospital, with the government revealing it wants to build a new hospital instead of redeveloping it.

Opposition health spokeswoman Giulia Jones said the government had a track record of failing to deliver critical health infrastructure.

"Government briefs have recently revealed an impending shortfall of hospital capacity in our growing north, and now it appears expansions to the Canberra Hospital in the south are being further delayed," she said.

"It's time for Labor and the Greens to stop talking about hospital expansions and start delivering them."