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 Australian locations will 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 seven active infections.
Those cases are all in isolation and have prompted about 40 potential exposure sites, including a number of flights from Sydney and Melbourne, supermarkets, shopping centres and hotels in Adelaide and the Adelaide casino.
However, no new infections were reported on Sunday.
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.
Premier Steven Marshall said SA had moved very quickly to increase the quarantine arrangements for all international travellers.
"We are concerned but at this stage, we are trying to determine what will occur with this new variant," he said.
"We need a few more weeks to understand the Omicron variant. We need to understand how our current levels of vaccination will protect us.
"We also need to know what the symptoms are likely to be.
"At the moment we know it is highly transmissible but we don't have much information beyond that."
Mr Marshall said the new cases in SA detected in travellers from interstate were "inevitable" once the state relaxed its border rules.
"At the moment everything is going to plan," he said.
Australian Associated Press