The virus was first detected in a patient in the ward who was found to be positive during routine testing. It is not yet known how that patient contracted COVID-19.

Canberra Hospital Cancer Centre clinical director Paul Craft said authorities were still investigating how COVID-19 had spread throughout the ward. He said this could take some time.

"It's been a little difficult to track where the virus has spread through the population since then, we're still working on that," Dr Craft told ABC Radio.

"It will probably be a long time before it's exactly clear how the outbreak occurred."

Dr Craft said it had been four days since a new case had been detected in the ward. He said authorities believed the outbreak would be suppressed by the end of the week.

The ward is closed to new admissions until the outbreak is contained.

MORE HEALTH NEWS:

Health Minister Rachel Stephen-Smith revealed the outbreak in the cancer ward on Monday.

"We do have an outbreak in one of our cancer wards in Canberra Hospital at the moment, which is obviously a significant cause of concern for those people and their families," Ms Stephen-Smith said.

"That is being treated very seriously."

The outbreak had contributed to a rise in COVID hospitalisations which were at a record-high on Sunday night.

Dr Craft said none of the patients in the cancer ward have developed severe COVID-19 disease. He said all those who tested positive were treated promptly with antiviral treatment.

"The people who developed the virus in the ward have all been able to access very timely antiviral treatment and we're confident they've done well, we haven't had any patient yet who has developed severe COVID disease or has been required to transfer to the COVID ward or anyone needing anything like ICU treatment so we're hoping out patients will make a speedy recovery," he said.

The outbreak has come amid increasing pressures on hospitals, with facilities expected to remain under immense strain for the rest of winter.

Our coverage of the health and safety aspects of this outbreak of COVID-19 in the ACT is free for anyone to access. However, we depend on subscription revenue to support our journalism. If you are able, please subscribe here. If you are already a subscriber, thank you for your support. You can also sign up for our newsletters for regular updates.

We've made it a whole lot easier for you to have your say. Our new comment platform requires only one log-in to access articles and to join the discussion on The Canberra Times website. Find out how to register so you can enjoy civil, friendly and engaging discussions. See our moderation policy here.