South Australia announces six-day 'circuit-breaker' lockdown

South Australian Premier Steven Marshall has plunged his state into full lockdown for six days to get on top of a growing COVID-19 cluster in Adelaide.

The lockdown will begin at midnight on Wednesday with police set to enforce the tight restrictions which include allowing only one person per household out of their homes once a day.

"I have long said that COVID has challenged us but not beaten us. We continue to face our biggest test to date. We must rise to this challenge and rise we are stopping each and everyone of us united with a common purpose to beat this silent enemy," Mr Marshall said.

Mr Marshall said he was "going hard" and early.

"Time is of the essence. And we must act swiftly and decisively, we cannot wait to see how bad this becomes," he said.

"We need a circuit-breaker to stay ahead of this. We need breathing space for a contact tracing blitz to protect the elderly, to protect the vulnerable, to protect our entire community.

"There is no second chance to stop a second wave. We are at a critical point, but we will get through this."

Mr Marshall said South Australia has "one chance" at crushing the wave of COVID-19 cases.

"We know that these restrictions are going to be very punishing on the people of South Australia. But we also know that we’re doing it for the right reasons to stop a far harsher lockdown which could come if we allow this virus to get away," he said.

Chief Health Officer Nicola Spurrier said the hard lockdown was critical to avoid seeing a similar outbreak to Victoria's second wave.

"If we leave this any longer … then we’re going to be in this for the long haul and we will be like the experience in Victoria, where we get increasing cases every single day, and we have to go into a significant lockdown for a very long period of time to snuff it out and and to get rid of every last bit of community transmission," she said.

"In the early days we thought we would have this one large wave and we had no idea how long it would last. I was really surprised it was only very short and we managed to suppress it very quickly and get on top of it.

"Clearly, if it is reintroduced into a community, it takes off very quickly and that is exactly what had happened in Victoria. I don't want that to happen here in South Australia and I am going to do everything possible to make sure that that doesn't happen."

Professor Spurrier said the Parafield cluster at the centre of the state's outbreak had now grown to 22 cases with two new infections added to the total.

"There are also an additional seven people who are either awaiting test results or we had an initial test that was negative but we are highly suspicious and treating them as infectious," she said.

Professor Spurrier acknowledged the restrictions were significant.

"I would call it a circuit-breaker, I mean it really is extreme," she said.

"We are really at the beginning of this in South Australia and I need everybody to basically find a safe place to be for the next six days and stay there, as much as possible. Whether this is a Netflix blitz for some people… I know it’s going to be really difficult for many people, but we just all need to be doing it.

"It is too early to tell but this is really the one chance we have got to having a normal Christmas. If we leave it too much longer than that chance disappears."

She singled out the Woodville Pizza Bar as a site of concern and asked anyone who had received a takeaway delivery from the venue between the November 6 and November 16 to self-quarantine and get tested.

She said credit card records were being examined to track down customers of the pizza bar.

Professor Spurrier said one case has been discovered in a kitchen hand at the Stamford Hotel, which confused authorities.

Investigations determined the man was a close contact of a part-time worker at the Woodville Pizza Bar who worked as a security guard from the original outbreak Peppers hotel.

"We want people for the next six days to go home, make sure they’ve got their supplies, and to really spend as much time in that one place as they possibly can, leaving just for essential food, essential medical requirements and the like," Professor Spurrier said.

"You need will be thinking about where you are going to be for the next six days, we would be the most convenient for you where you can look after your loved ones."

South Australia police commissioner Grant Stevens said more information on enforcement would be made available later on Wednesday.

"You are required to stay at home for the next six days. One person from a home may leave once a day to obtain groceries [and] supermarket supplies. You may leave to provide care and support for another person where it is essential, [including] medical services," he said.

"We expect people to do the right thing and we are relying on people to do the right thing. We will support the community as much as we can but if you deliberately disobey the restrictions, if you essentially ignore the advice you were given, you should expect we will take action. We don't want to do that [we want] to work with the community and everyone is in the same boat," he said.

He said that critical infrastructure and essential services including supermarkets and petrol stations would remain open.

Commissioner Stevens said there was no need for panic buying.

"I do think people are going to flood our supermarkets. This afternoon is going to be a particularly challenging time for our retail outlets," he said.

"Supermarkets are going to be open beyond today. There is no need for people to rush to supermarkets [today].

"There is no permission to leave home to exercise for the next six days. If you deliberately disobey these restrictions, if you essentially ignore the advice that you’re given then you should expect that we’re going to take action."