The partial bypass started at midday and will continue to about 4pm.

"At the moment one of the sticking points is the high number of patients who are very unwell and are unable to go home," a Canberra Health Services spokeswoman said.

"This creates a backlog situation for the hospital when an increasing number of patients come to the emergency department."

The spokeswoman said people should only attend the emergency department in a genuine emergency.

She said patients should attend a walk-in centre or their GP for other medical care.

"Our doctors and nurses at the front line are working tremendously hard at the moment to help with the flow of patients and getting treatments under way," the spokeswoman said

"We appreciate that this pressure can have an impact on people at the ED, but we also remind the public to be patient and kind to our front-line staff. They're there to help and provide the best clinical care for our community."

During a bypass ambulances are forced to take patients in stable conditions to Calvary Hospital.

Meanwhile, trauma patients, paediatrics patients, and patients facing life-threatening emergencies will still be taken directly to Canberra Hospital.

Canberra Health Services took to Twitter to announce the hospital was experiencing "very high" demand.

"We remind all Canberrans that emergency departments are for emergencies and urgent treatment."

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Canberra Hospital last bypassed patients to Calvary Hospital in November to ease pressure on the emergency department.

Capacity problems have plagued the hospital recently, with numerous bypasses occurring in the winter of 2019.