Victoria has declared an emergency across all Melbourne hospitals as the Omicron wave impacts health services.
The so-called Code Brown will come into effect on Wednesday at midday and is aimed at relieving pressure on the system brought on by rising admissions and staff shortages.
The order, which will also apply to six regional hospitals, will mean some hospital staff could be recalled from leave and non-essential care could be deferred.
It's usually introduced in the wake of an external emergency, such as transport accidents, chemical spills and natural emergencies.
It comes as the federal government announced it would be activating an agreement to make private hospital staff available to help COVID-affected areas.
The agreement - which was established in April 2020 - will see up to 57,000 nurses and more than 100,000 staff made available to affected areas around the country.
"It's a workforce which is skilled, planned, appropriate and available," Health Minister Greg Hunt told reporters on Tuesday.
"The states and territories will, where necessary, work directly with the staff and with the hospitals themselves ... it will be up to the states and territories to activate those."
Mr Hunt said taking this step was "planned, prepared and anticipated", and triggered by "any surge in either case numbers or hospital numbers".
The national medical stockpile has also been activated to support states and territories with personal protective equipment shortages.
Chief Medical Officer Professor Paul Kelly said the healthcare sector had been preparing for workforce pressure for some time.
"This is the first time the health system has come under pressure to the extent that we're seeing in the last week or two," he said.
Victoria's Deputy Premier James Merlino said: "We've reached a point in our health system where it's juggling severe workforce shortages - we have got more than 4,000 healthcare workers unavailable right now - alongside a vast number of patients with COVID-19 who require hospitalisation."
"Our hospital system is under extreme pressure.
"This is all happening alongside the need to treat patients with urgent and emergency needs."
The declaration - which covers hospitals in Barwon, Ballarat, Bendigo, Shepparton, Albury and Latrobe - is expected to last from four to six weeks and will ease pressure on the system ahead of the expected peak of hospital cases.
It is the first time the Victorian health system is having a system-wide Code Brown. They are usually reserved for short-term emergencies, such as the Black Saturday bushfires and deadly 2016 thunderstorm asthma event.
Some 1,152 people are in hospital with the virus in Victoria - lower than Monday's figure of 1,229 - and 127 of them in intensive care, 43 on ventilators.
Mr Merlino said: "While it's good to see hospitalisations slightly lower today, you've got to look at the trend and where we're going to head to.
"It's basically been steadily climbing over the last week or so and we know that the biggest increases are yet to come."
He added hospitalisations in NSW, where the Omicron outbreak is a couple of weeks ahead of Victoria, continue to increase by about 100 people per day.
"If we see what we've been seeing in NSW, we could well get to over 2,500 hospitalisations and more over the next few weeks so now is the right time to implement this plan," he said.