Doctors and other healthcare staff working in a number of Victorian hospitals may be recalled from leave or reassigned, the state government has announced.

For the first time on Tuesday, the Victorian Government declared a code brown emergency for all its Melbourne hospitals and six in the regions.

As well as staff being recalled or redeployed, the hospitals will be required to postpone or defer care that was not urgent, said acting Minister for Health James Merlino.

The measure would come into effect from midday on Wednesday and last for four to six weeks as hospitalisations are expected to peak.