The capacity issues come before peak flu season has even hit, which last year put unprecedented pressure on Canberra'a emergency departments.

A fax was sent to all Canberra, Queanbeyan, Jerrabomberra, Bungendore and Braidwood GPs last week asking them to consider alternatives before referring a patient to the emergency department.

Opposition health spokeswoman Vicki Dunne said it was a dangerous directive that showed a lack of planning from the government.

ACT Health did not answer questions from The Canberra Times asking if there was a reason for the high demand and if it meant the department was under-resourced.

Instead it pointed to budget announcements and reminded people of the alternatives for non-life threatening conditions.

The fax came at a time when the hospital was at "bed block" and the emergency department full.

It said the hospital was experiencing very high levels of service demand and patient acuity.

"Of course we all want to have the best care for the patients under our care, however we are seeking your support as we seek to manage this demand and acuity such that services are available for those most in need," the letter read.

It also asked GPs to contact the admitting officer for advice before referring patients to the ED.

ACT Australian Medical Association president and GP Antonio Di Dio said he supported Canberra Hospital's directive to GPs, but said winter would be a testing time.

"If in time of huge demand like this when the ED is struggling, it is vital for hospital administrators and the government to have access to the best possible resources and enough of them," he said.

"Winter will be testing and hence announcements in the budget about additional beds.

"Bed block in the ED isn't caused by walk-in centres and low acuity patients sitting in ED,  it's caused by lack of beds to admit to.

"Winter will be testing and we warned when the budget was announced that government will need to monitor demand for additional beds very closely."

Mrs Dunne claimed the directive was dangerous and could cause a rush at nurse-led walk-in centres, which would in turn refer back to GPs or emergency departments.

She said the "roundabout" delays to treatment could put patient lives at risk.

“Our hospitals are under maximum pressure and Minister Meegan Fitzharris has not responded to the warning signs," Mrs Dunne said.

“Last year, the Canberra Hospital emergency department was in crisis mode for three months in a row after an alert level three was triggered.

“But the Minister waved the crisis off saying a bad flu season was to blame.

“We are not even in the throes of the flu season and already our hospital is struggling to cope with demand.

“History looks set to repeat itself.

“Our hard working and dedicated nurses, doctors and hospital staff continue to be under-supported
by Minister Fitzharris’ poor planning."

An ACT Health spokesman said the fax was just one of a number of "routine" operational measures taken during a period of high demand.

"As we move into the winter season, Canberra Hospital and Health Services will experience an increase in the volume and acuity of patients," he said.

"We would like to remind the community that there are a range of health service options available for people with non-life or limb threatening injuries/illnesses. We would encourage people to use these alternatives where appropriate."

ACT Health pointed to recent funding announcements for Canberra Hospital,  including $11.5 million to be spent in the coming financial year to support the emergency department, intensive care and more in-patient hospital beds.