South Australia will no longer allow visitors from New South Wales and the ACT from July 20 as planned.
Premier Steven Marshall said the border will remain closed as Sydney battles a growing cluster linked to a pub in the south-west of the city.
Victorians are also banned from South Australia but residents from other states can enter without having to quarantine.
South Australia will no longer allow visitors from New South Wales and the ACT on July 20 as planned
'We know that this is going to be very inconvenient to people who have already made plans,' Mr Marshall said.
'But our primary responsibility is for the health, safety and welfare of all South Australians.
'We're being cautious, we're looking at the epidemiology of what's going on, we're looking at the results in NSW.
'But at this stage, there's too much uncertainty.'
SA's decision will also impact on AFL teams planning to travel to Adelaide from Sydney.
The state previously lifted the quarantine restrictions for people coming from Queensland, Tasmania, the Northern Territory and Western Australia.
But it has imposed a hard border closure with Victoria, only allowing locals to return and essential travellers through, because of the surge of infections in Melbourne.
Mr Marshall said South Australia was still 'a long way off' imposing a similar hard border closure with NSW.
From Saturday, the state government will start charging Australians returning from overseas for the cost of their 14 days of supervised quarantine.
The premier said SA was still keen to participate with the national repatriation program but those arriving from Saturday would be asked to pay for their hotel stay.
Individuals will be charged $3,000, with their partners to be billed $1,000 and $500 for each child.