Three ambulances were diverted from Canberra Hospital on Monday during a bypass.
All ambulances carried one patient each during the bypass which occurred from midday to 4pm.
Canberra Hospital reached capacity, triggering a bypass where patients in stable conditions were transported to Calvary Hospital.
ACT Health reported 278 people went to the emergency department on Monday.
A Canberra Health Services spokesperson said the hospital had a large number of very unwell patients who were unable to be discharged, coupled with an increase of unwell patients presenting at the emergency department.
Canberra Hospital has faced two bypasses in a month, with a similar bypass occurring on November 18.
The hospital faced multiple bypasses during winter last year.
Australian Medical Association ACT president Antonio Di Dio said Monday's bypass was a result of unusually high demand.
"I think we should probably give them the benefit of the doubt," Dr Di Dio said.
"I don't think there's a single occasion that you could criticise a single staff member in emergency for that happening."
Despite unprecedented demand, Dr Di Dio said the bypass highlighted ongoing troubles at Canberra Hospital.
"Every time this happens it gives us an opportunity as citizens and healthcare consumers to ask ourselves what are the limitations of our services," he said.
"How much can we expect from them? Are there any structural problems there which we can help support?"
Dr Di Dio singled out the number of beds and waiting times as key structural issues.
"It's really simple, we've got a very similar number of beds to 400,000 living in Canberra as we had years ago when there were only 300,000 people living in Canberra," he said.
"[Regarding waiting times] Canberra Hospital falls significantly below national benchmarks.
"Even though I believe we should be very supportive of what happened yesterday I think it's a good reminder to look at those national benchmarks and ask ourselves why we aren't doing as well as we should.
"There are enough doctors and enough nurses and enough staff in emergency and they're all really good.
"But when they see a patient and then make a decision whether the patient needs to stay in hospital or not the patient is waiting too long."
Opposition health spokesperson Giulia Jones said Monday's bypass shows the capacity and workplace pressures at Canberra Hospital.
"Labor and the Greens have spent the last decade talking about expanding the Canberra hospital yet we are still waiting for the first sod to be turned," she said.
"Until their words are followed up with action these events will continue to occur."
