South Australia is waking up to its first morning under lockdown.

For the next six days, people will only be allowed to leave their homes for medical care, to work in essential services, or to obtain medical supplies.

Schools, gyms, eateries, factories and construction sites are closing, exercise isn't permitted outside the home - and weddings and funerals can't be held.

Officials hope the short, sharp lockdown will contain a cluster of the virus in Adelaide.

ABC Adelaide's Rhett Burnie told Mike Hosking the state has gone from Covid-free to full lockdown in a matter of days.

"Many people are in shock about how quickly the situation has changed."

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