The government says lockdown on community activities will work to significantly reduce the risk of the virus spreading further.

Acting prime minister Michael McCormack said COVID outbreaks like the latest being managed in South Australia are to be expected, but it remains the responsibility of all Australians to continue to do their part through this health pandemic.

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"The local tracking and tracing has been as it should be. They've tested thousands upon thousands of people in Adelaide particularly in the northern suburbs to isolate this outbreak.

"We will get outbreaks. In NSW we've had 11 days in a row of no cases and that's a fantastic situation. In the United States of America last Wednesday, 200,000 cases, on the day when the world suffered its greatest mortality rate since COVID began and that is very, very sad.

"Nearly a million and a half people dead from COVID-19 - in Australia 907.

"We've done very well as a nation and I thank all Australians for doing all the things they need to do - downloading the app, maintaining social distancing, washing hands regularly, going and getting tested if you have flu-like symptoms.

"That's what Australians need to continue to do. We will get a vaccine.

"Australia has spent a lot of money. The Commonwealth government is investing in four vaccines at the moment and if better vaccines come on we will have discussions about those too.

"We want to make sure that when the vaccine becomes available that it is available not just for all Australians, but for all those in the Pacific Islands. We want our nation and our region to be its best self through COVID-19 and we've done that so far.

"I'm glad the Premier of NSW has made an eminently sensible decision not to close the borders to South Australia at the moment.

"It's a situation that is in hand and we will continue to monitor it. We are there to help any state government."

In South Australia from Thursday, all schools are closed along with universities, pubs, cafes, retail stores, food courts and takeaway food outlets.

Regional travel is banned and aged care centres are in lockdown.

Factories are closed, along with the construction industry, and elective surgery has ceased.

Weddings and funerals are banned along with all outdoor sport and exercise and masks will be required outside the home.

People who are not essential workers will only be allowed to leave their homes once each day to buy groceries or to seek a COVID-19 test or other medical treatment.

Supermarkets, petrol stations, medical centres, critical infrastructure, public transport, airport and freight services, banks, post offices, school and childcare for essential workers and veterinary services are open.

Meanwhile, Australia's peak medical body says it is too soon for a mass return to the office and public transport.

Australian Medical Association president Omar Khorshid said the growing Adelaide COVID-19 cluster showed Australia was not out of the woods yet.

"While infection numbers generally give us cause for optimism, the South Australian outbreak this week shows that the virus is still in the community," Dr Khorshid said.

"The only way to keep these numbers low is to continue to follow the habits that have proven so effective in getting Australia to such an enviable position."