South Australia will go into lockdown from midnight on Thursday.
The extreme restrictions will last for six days and will be followed by a further eight days of reduced restrictions.
South Australian Chief Public Health Officer Nicola Spurrier has warned there is only a "very small window" to stamp the virus out.
Here's what you need to know.
What's closing down?
All schools will close from Thursday, except for the children of essential workers and vulnerable students.
Universities will have to close too.
All outdoor exercise and sport will be banned.
Aged care and disability care facilities will all go into lockdown, but end-of-life visits will be allowed.
All hospitality businesses — including takeaway food and food courts — will need to close.
Elective surgeries will be postponed, except for urgent operations and cancer treatment.
The construction industry will not be allowed to operate, while open inspections and house auctions will be cancelled.
Holiday homes will not be available for lease, and weddings and funerals will be banned for the full six days.
What's staying open?
Supermarkets and bottle shops will stay open.
Medical services, including mental health services, will also be available, as will veterinary services.
Childcare centres will be allowed to operate, but only for families of essential workers.
Essential services like water, power and telecommunications services will keep running, along with essential aspects of mining, smelting and large factory operations.
Public transport, airport and freight services will all continue to operate, as will petrol stations, banks and post offices.
Am I allowed to leave the house?
Everyone must stay at home, except when completing essential activities.
Essential workers will be allowed to travel to and from work.
You will be allowed to leave the house to seek medical care or provide care for another person.
One person per household will be allowed to shop for food once per day.
What else do I need to know?
Health authorities want masks to be worn everywhere outside the home.
Interstate travel is strongly discouraged.
Anyone who is currently on holiday within South Australia has been told to decide where they would like to spend the next six days.
In other words, if you're visiting a holiday house or on a camping trip away from home and decide to stay there, you'll need to stay there for six days after midnight.
