The wearing of face masks will be mandatory in Victoria's worst-hit coronavirus areas from 11.59pm on Wednesday night.

"If you are out of your home for one of the four permitted reasons, then you need to be wearing a mask and I stress – or a face covering," Premier Daniel Andrews announced today.

"It need to stress it need not be a hospital-grade mask, it need not be one of the handmade masks like I was wearing when I came in today. It can be a scarf, it can be a home-made mask."

Anyone in Greater Melbourne or Mitchell Shire caught without a mask or face covering will be fined $200.

Andrews said an order of at least 2.5 million masks was on its way to Melbourne, with the "first significant batch" expected to arrive this week.

He told reporters "common sense" will guide when people need to don a mask, adding the decision had been made on the advice of Victoria's chief health officer Prof Brett Sutton.

"It's a relatively simple thing but it's also about embedding behaviour, which I think is just as important on the other side of this second wave as it is in bringing these case numbers down," Andrews said.

"We're going to be wearing masks in Victoria and potentially in other parts of the country for a very long time. There's no vaccine to this wildly infectious virus and it's a simple thing, but it's about changing habits, it's about becoming a simple part of your routine.

"Most of us wouldn't leave home without our keys, we wouldn't leave our home without our mobile phone. You won't be able to leave home without your mask and then wear it where it is absolutely essential to stop the spread of this virus."

Victoria's Health Minister Jenny Mikakos said the mandating of mark usage is an "important tool that we will use to minimise the spread of this virus".

The Victoria Premier announced three more people have died from coronavirus in Victoria overnight, and an additional 363 new infections have been reported in the past 24 hours – taking the state's total case tally to 5696.

Sutton said everyone over the age of 12 is recommended to wear a mask.

"That is in recognition that it's likely to work for all of those age groups. Below the age of 12, it's a consideration. We say not for toddlers. So not for 2 years and below," he said.

"It's a consideration for all other children. But it is mandatory, really, from that high school age onwards."

Exemptions will be given to people who cannot wear a mask due to a medical condition, and when engaged in an activity where it is "entirely impractical" to wear a mask, it's also not a requirement, Prof Sutton said.

"But it does make a difference. And having universal mask wearing is the key here, because not only are you – if you're potentially infected – shedding less virus into the atmosphere, but the person around you, if they're 1.5 metres away or closer, or further away, will be less exposed," he said.

"And if there's virus out there in the atmosphere, there's some filtering that happens with those cloth masks and as we say, it doesn't have to be a mask. It's a cloth face covering. It does need to cover the nose and mouth, and as some of you might have seen, masks don't do very well in your pocket. They don't do very well when sitting on your chin. They do need to cover your mouth to work properly, so that really needs to be reinforced."

Sutton said that while "obviously, if you're drinking or eating, you're not going to wear the mask". For the rest of the time Victorians should.

"These won't always be really easy and they won't always be welcome, but they are important, and there are lessons, increasingly internationally, about the jurisdictions that are doing well have introduced mandatory mask wearing," he explained.

"And those that haven't are the ones that are seeing really catastrophic numbers at the moment."

People wearing a mask should avoid touching it "as much as you can avoid it", and to wash their hands before and after putting on their mask with soap and water or alcohol-based hand sanitiser.