Australia has seen another day of rising Covid-19 cases and hospital admissions amid fears that changes to testing requirements could mask the full scale of the outbreak.

The country reported 72,000 cases on Thursday, up from 64,000 a day earlier, while hospital admissions jumped to 3,267 from 2,990. The number of patients in intensive care rose to 208 from 196.

The state of Victoria recorded six deaths and 21,997 new cases, the biggest daily jump in cases since the pandemic began.

Queensland reported more than 10,000 cases as health officials warned that many more undetected cases were probably spreading in the community.

New South Wales saw 34,994 new cases, slightly down from the record number of 35,054 on Wednesday. A double-vaccinated man in his 20s was among six deaths reported on Thursday in Australia's most populous state.

The case numbers do not necessarily reflect the true spread of the virus as they only count the number of recorded cases.

Prime Minister Scott Morrison defended a new policy that Australians no longer need to take a PCR test to confirm a positive rapid antigen test. The change was made in a national cabinet meeting with state and territory leaders on Wednesday.

"Case numbers are less of an issue," Mr Morrison said. "It is connecting to care that is the issue, and the Commonwealth provides telehealth support to people to be able to do that and get advice on how they can manage their infection at home and, should matters escalate, to seek further assistance."

Health minister Martin Foley said people are required to report positive rapid antigen test results to the Department of Health. Any person who has received a positive result on a rapid antigen test will be treated as a probable case and will have to isolate.

Because most rapid antigen tests are carried out at home, experts fear the new policy will lead to an underreporting of cases. They say an accurate picture of case numbers is necessary to ensure the preparedness of hospitals and other medical facilities.

University of Melbourne epidemiologist Professor Tony Blakely said the move away from confirmatory PCR tests would mean case numbers would not be accurate in the future.

"The horse has bolted, this is the biggest policy failure so far in Australia," Prof Blakely said. "We also haven't thought about how you can load up that data to the surveillance system, so we won't get that in place in the next couple of weeks."

Mr Morrison also faced questions about the Australia Border Force's decision to revoke a visa granted to Novak Djokovic ahead of the Australian Open.

The Serbian tennis star had been granted a medical exemption to play at the Australian Open. Many Australians who have struggled to obtain sparsely available and often expensive rapid antigen tests, or who have been forced into isolation, saw a double standard in the country's treatment of the tennis player.

Mr Morrison denied that Djokovic was singled out when asked whether the subsequent cancellation of his visa was political and based on his prominence as a sports star.

"One of the things the Border Force does is they act on intelligence to direct their attention to potential arrivals," he said. "When you get people making public statements about what they say they have, and they're going to do, they draw significant attention to themselves."