As local COVID-19 cases in Australian states of New South Wales (NSW) and Victoria continued to grow, stricter border restrictions are in place across Australia from the first day of the new year.

At midnight of the New Year's eve, anyone who has been in NSW in the preceding 14 days are prohibited from entry into the neighbouring state of South Australia, unless they are essential travellers, South Australia residents or just transiting in and through NSW.

"It is still not clear where the Northern Beaches cluster started from and that means there may be some chains of transmissions in other parts of NSW that haven't surfaced yet," said South Australia's Public Health Chief Officer Nicola Spurrier.

From Saturday, people travelling from NSW cannot enter Victoria either. Victorians who arrive back from NSW after the deadline will be turned back at the border or need to go into hotel quarantine.

The Northern Territory also listed Greater Sydney as a hotspot instead of the previous seven Sydney suburbs. Anyone from Greater Sydney needs to go into mandatory quarantine while entering the Northern Territory.

NSW, with Sydney as the capital city, recorded three new locally acquired cases in Western Sydney in the 24 hours to 8 p.m. Thursday night, with no links to the Northern Beaches cluster. Two new cases were recorded in returned travellers in hotel quarantine. Infectious source of two new local cases are still under investigation.

A number of new venues were added into the list of public health alert where the confirmed COVID cases visited.

"A strong message to all of us across NSW is to be high alert, to come forward and get tested with the modest symptoms," said NSW Premier Gladys Berejiklian.

At the same time, travellers from Victoria, which recorded five locally acquired cases and three international acquired cases in quarantine on Friday, were banned from entry into the state of West Australia from midnight of the New Year's eve.