South Australia looks set to impose tighter COVID-19 restrictions on NSW in response to the growing virus cases across Sydney.
Police Commissioner Grant Stevens says anyone considering travelling from SA to NSW in coming days should seriously consider if their trip is essential.
He says South Australians on holiday or travelling in NSW should also consider returning home as soon as possible.
It suggests SA could move as early as Thursday to tighten the border rules.
"The situation is volatile and changing rapidly." a police statement said.
"The continued spread of cases in New South Wales is of particular concern."
At present, only people from Sydney's northern beaches are banned from entering SA.
Those from greater Sydney, the Central Coast and the Wollongong region can come but must quarantine for 14 days.
People from other areas of NSW must submit to a COVID-19 test.
The warnings came on Wednesday as NSW reported 18 new cases of community transmission including six linked to a new cluster in Sydney's inner-west.
At the same time, the number of active coronavirus infections in South Australia jumped to eight with three new cases reported.
SA Health said a man in his 30s, a man in his 50s and a child had all tested positive after recently returning from overseas.
They remain in a quarantine hotel in Adelaide.
All of SA's eight active cases were acquired overseas.
The state has now had a total of 575 cases since the start of the pandemic.