Coronavirus hot spots in Melbourne's inner north and west have been put into lockdown in an effort to contain an outbreak of the deadly disease in Victoria.
Much like earlier stage three restrictions, people in these postcodes will only be able to leave their homes for four reasons: for care or caregiving, to exercise, to purchase food and other essential items, or to go to work or school.
Cafes and restaurants will only be open for takeaway and delivery.
Tough border measures will also be introduced for anyone coming from Victoria, including mandatory hotel quarantine.
"If we don't take these steps now we will finish up in a situation (where rather) than locking down 10 postcodes, we will be locking down every postcode", said Andrews, referring to postal codes which cover the 36 suburbs.
"(But) we've got to protect the people of South Australia - we are not prepared to go backwards".
The return to lockdown is a devastating setback for the home state of almost a quarter of Australia's 25 million people, widely seen to have taken one of the toughest enforcement approaches when the country first went into lockdown in March.
The surge in Covid-19 cases in Victoria and strict new quarantine regulations issued by the Queensland government has thrown the recently-recommenced football seasons into chaos, with the AFL forced into a last-minute change of this week's fixture.
It comes as Victoria recorded 64 new COVID-19 cases in the last 24 hours, bringing the total of 233 new cases in the state since last Thursday. By comparison, the most populous state, neighboring New South Wales, and the third-most populous, Queensland, both reported no new cases.
He said police would be actively enforcing the suburban lockdown.
"It will be a devastating impact on people and particularly local businesses, but we have to do it", he added.
SA Premier Steven Marshall said on Tuesday the state will not proceed with plans to open its border to Victoria on July 20.
They will also need to quarantine for 14 days upon returning to Queensland from playing a game in Melbourne, or if they have played in another state against a team from Melbourne.