Wearing a mask will be compulsory for people living in Victoria's locked down areas as an inspection blitz of at-risk workplaces begins.

Efforts to control Victoria's alarming COVID cases have ramped up with Melburnians told to wear a mask whenever they leave the house.

Premier Daniel Andrews on Sunday announced the new measure, which will come into effect from 11.59pm on Wednesday for residents of metropolitan Melbourne and Mitchell Shire.

The two areas remain in lockdown, with people only allowed to leave their homes to exercise, buy groceries, care or care-giving and to go to work or school if they cannot do so from home.

"If you are out of your home for one of the four reasons, then you need to be wearing a mask and I stress - or a face covering - it need not be a hospital grade mask, it need not be one of the handmade masks," Mr Andrews said on Sunday.

"Any face covering is better than no face-covering."

The premier also announced an inspection blitz of at-risk workplaces after it was revealed about 80 per cent of new cases since mid-May are linked to workplaces.

The crackdown will include distribution centres, call centres and meat processing centres and be done by police and WorkSafe.

Victoria on Sunday recorded 363 new cases of the virus and two more deaths, taking the state's toll to 38, with more infections cropping up in nursing homes.

Thirty-eight cases and now linked to Estia Health in Ardeer and 24 have been connected to Glendale Aged Care facility in Werribee.

Aged care workers are being urged to stop working across multiple sites in a bid to stop the virus spreading further.

Health Minister Greg Hunt announced on Sunday said the Commonwealth would inject cash into Victoria's aged care sector to ensure staff can earn more working at just one centre.

He said the funding was necessary to protect aged care residents and staff, noting many cases were a result of outbreaks caused by hotel quarantine breaches.

"In order to protect these residents and the staff, most of whom have contracted the virus within the community following the catastrophic breach of hotel quarantine that has seen a city of five million in lockdown," Mr Hunt said.

His comments come as the inquiry into Victoria's now infamous hotel quarantine program starts on Monday.

The probe will be led by retired judge Jennifer Coate, assisted by Tony Neal QC.