South Australia has tightened its border rules following the emergence of the Omicron COVID-19 variant.

All international travellers and people arriving in SA from high-risk locations in Australia will once again be required to quarantine for 14 days.

People arriving from lower-risk locations interstate must also have a coronavirus test within the 72 hours prior to arrival and must show proof of a negative result.

The provision for people to have a COVID-19 test after they arrive in SA and isolate until they get a negative result has been removed.

The changes come days after SA lifted most of its border restrictions, which led to a number of infections being detected in interstate arrivals.

With three new cases on Saturday, the state is currently managing eight active infections.

Australia has shut its borders to nine southern African countries and NSW, Victoria, SA and the ACT have brought in new rules for all international arrivals amid concern over Omicron.

Urgent genomic sequencing is also under way to determine whether two people, who tested positive for the virus in Sydney overnight after spending time in Africa, have the variant.

-AAP