Victoria is slashing elective surgery in hospitals across the state in response to rising numbers of patients with COVID-19.

Non-urgent surgery will be reduced in public and private hospitals from Thursday as the health system comes under extreme pressure amid the rampant spread of the Omicron variant.

All emergency and urgent elective surgery will continue.

Elective procedures where the patient is already scheduled for admission on Friday and Saturday may still be able to go ahead, where it is not safe or logistically possible to postpone.

Private hospitals were allowed to increase their non-urgent surgery cap by a quarter to 75 per cent in November, while some public hospitals could resume operating at 50 per cent.

The health department said the latest change would reduce the burden placed on hospitals by the new strain and ensure the system can meet demand.

"These changes will enable public and private hospitals to work as one system to make the best use of available capacity," it said.

"Those waiting for non-urgent elective surgery who are impacted by the changes are encouraged to reach out to their general practitioner should their condition in any way deteriorate, so they can be reviewed and re-prioritised to a more urgent category if required."

On Monday, three Melbourne hospitals told people not to visit emergency departments unless "absolutely necessary" due to extreme pressure from rising COVID-19 admissions and demand for testing.

There are currently 591 people in hospital with COVID-19 across the state, up almost 200 from a week ago.

Elective surgery levels will continue to be reviewed to ensure their are enough beds for COVID patients, the health department said.