Hospital staff moved 60 patients when smoke spilled into its buildings and power to some areas was cut off following a switchboard fire on Wednesday night.

In chaotic scenes, fire fighters had to search for the source of the fire when multiple alarms went off, while staff moved patients from buildings.

The Canberra Hospital Switchboard was unavailable and emergency services asked people to contact patients and staff on personal mobiles.

Emergency services, ActewAGL and ACT Health worked through the night as power was restored to the hospital's main patient and administrative areas.

The hospital on Thursday cancelled outpatient clinics and elective surgeries and closed Hospital Road, while its emergency department restricted its services to major trauma cases and directed people self-presenting for care to the Calvary Hospital.

Relatives of patients, except for the critically ill, were asked not to visit their loved ones as the hospital dealt with the aftermath of the emergency.

Shadow health minister Vicki Dunne blamed the ACT government's neglect of the territory's health system for Wednesday's fire at Canberra Hospital.

"A decade and a half of neglect and under-investment has resulted in the closure of much of the Canberra Hospital, putting Canberrans in danger," Ms Dunne said.

"We have clear problems that have put people in jeopardy."

At a press conference on Thursday, Health Minister Meegan Fitzharris said the government's number one priority was patient and staff safety.

"I will be certainly making sure that we understand the incident and what steps, if any, we need to take to make sure this doesn't happen again," Ms Fitzharris said.

She thanked the emergency departments for their handling of the crisis overnight.

The ACT Emergency Services Agency acting commissioner Mark Brown said firefighters were called to the incident about 5.40pm on Wednesday, where they extinguished an electrical fire at the hospital's electrical switchroom.

"It wasn't actually a large fire in itself," Mr Brown said.

"The problem then was some smoke had entered the hospital. What was a reasonably straightforward fire actually caused the problem, which was the power outage."

"The community can be confident in the response that the ACT government put in place last night."

ACT Health's incident controller Dr Andrew Pingilley said the problem wasn't backups failing but rather power being unable to reach the switchboards.

He said acutely ill patients would have been protected by battery backup and acute treatment areas, such as intensive care, were not substantially affected.

"It's a bit early to know whether there's any substantial impact on [patient] backlog," Mr Pingilley said.

Evacuations took place across building five on Wednesday evening. A number of people in buildings two and three were also relocated to areas not affected by smoke.

ACT ambulance chief officer Jon Quiggin said an inflatable field hospital was set up in the event of having to evacuate patients to other hospitals across Canberra or New South Wales.

A hospital employee who was working at the time said the initial response was confusing but staff soon got their act together.

"It started off as a bit of a shambles," they said.

"But we got under way sorting out which patients could go home and which ones needed transfers to other wards or hospitals.

"It ran pretty smoothly from that point. Under the circumstances we did a solid job."

They said staff received a solid workout trekking up and down stairs while the power was out.

"Everyone working last night has permission to skip the gym today.

"Ten flights of stairs with no lifts gets the calves going."

All elective surgery and outpatient services will be reinstated on Friday and appointments booked will proceed as planned. ACT Health is contacting patients whose surgery or appointments were affected on Thursday to reschedule.

Hospital Road reopened on Thursday afternoon.

There was a partial evacuation at Canberra Hospital earlier this week when an air conditioning unit malfunctioned, sending smoke out through air conditioning vents in the hospital.

"Some staff were moved behind fire doors for a limited time," an ACT government spokesperson said.

"The alarm was turned off promptly and affected patients and staff returned to their relevant areas."

Mr Pingilley said on Thursday the two incidents were not related.

People were reminded to stay up to date on any service changes at Canberra Hospital via the ESA website.