Labor leader Peter Malinauskas said he supported the government's decision and had complete faith in public health officials.

"We're going to back in their judgment, and never doubt their motives," he said.

"We're going to comply with their requests, not because it's easy, but because it's right.

"We're going to remain calm, steadfast and resolute in tackling this challenge in a way that only South Australians can.

"This is going to be a tough period - none of us have confronted anything like this before."

Mr Malinauskas said those people who might lose their jobs because of the shutdown "won't be forgotten", and described those continuing to work in essential services as "our quiet heroes".

"Particularly in our supermarkets and their distribution centres, I know tonight you are under extraordinary pressure," he said.

So far 23 cases have been linked to the coronavirus cluster in Adelaide's north, but another seven people are waiting on test results and are thought likely to be infected.

Officials are hoping the lockdown will act as a "circuit-breaker" and stop widespread community transmission.

Australian Associated Press