The mental health wards at the hospital were already significantly understaffed before the expansion, with almost a quarter of the required full-time permanent specialist roles unfilled.

There has also been a significant shortfall in psychiatry registrars, with doctors told just over half the required positions were filled as of the end of 2020.

Canberra Hospital has been struggling to deal with increasing mental health presentations, with some patients stuck for days in the emergency department waiting for an inpatient bed.

The government recently added surge capacity next to the short stay mental health ward to manage demand, however, doctors say they were not consulted and were caught by surprise about when extra patients turned up.

Australian Medical Association ACT president Antonio Di Dio said the situation had left junior doctors distressed, with significant staff shortages already taking a toll.

"The extra beds are welcome, but if you create an extra nine beds overnight without staff then all they are is a piece of furniture," he said.

"This is felt by all those Canberrans who cannot get their children treated with speed and dignity and efficiency that's required.

"In credit to ACT Health they responded to our concerns, but they are obviously hamstrung by their inability to identify and employ as many new psychiatrists as they need."

ACT Visiting Medical Officers' Association president Peter Hughes says there are doctors who can fill the nine vacant permanent specialist roles.

"They have had those positions open for years," he said.

"We are sure there would be interested visiting medical officers provided they were offered standard contracts not locums."

He said the hospital was instead intent on looking overseas for doctors willing to take on staff specialist roles.

"There is chronic under staffing at the moment and it's causing stress on psychiatrists and the registrars from what I understand," Dr Hughes said

"The work is increasing, they're opening more beds, there's more demand in the emergency department, but no increase in staff."

Dr Di Dio said there was a nation-wide shortage of psychiatrists but the situation was far worse at Canberra Hospital than elsewhere.

He said as of the end of 2020, just 24 of the 42 psychiatry registrar positions were filled.

"They have been understaffed now for years," he said.

"When the problem is for a month or two months or six months, you'd really feel for the bureaucrats in charge.

"But when it's been going on for years it's actually something deeper and we need to very much hold the administrators and government to account.

"The more overworked and stressed the junior psychiatrists are the less likely it is that anyone would want to apply for these roles.

"They find it easier to recruit than retain psychiatrists.

"Ever since the pioneering days of Dr Brian Hennessy, the brilliant man charged with starting a psychiatry service in Canberra in the 1960s, that profession has been beset by workforce challenges."

A Canberra Health Services spokeswoman said the extra beds were required to manage increased demand over the Christmas period.

She said no formal consultation was undertaken as they were not technically additional patients.

"However, since the registrars raised concerns, within 24 hours of the move, the space [next to the short stay unit] has not been used," she said.

"Rather the existing surge capacity [in another part of the hospital] has been used instead.

"These are not additional patients as they are already under the care of the psychiatric team and would alternatively be in the emergency department awaiting a bed for long periods of time.

"There has been the addition of one FTE consultant dedicated to the emergency department in the past 12 months, as well as an expansion of the consultation liaison team who support the general wards, with further expansion planned in the next three months."

The spokeswoman said there was a plan to cover all staff vacancies, with both visiting medical officers and careers medical officers used to fill them in the short term.

She said there would be a full complement of psychiatry registrars by next month, while denying the AMA's statement that only half were filled as of 2020.