Plans for Christmas reunions have been dashed around the country after states and territories moved to shut their borders to visitors from Sydney and surrounds.

Australians are waiting to see if the NSW government's strategy to "go hard, go early" on a coronavirus outbreak in Sydney's northern beaches area pays off.

Residents of NSW now face restrictions entering every other state and territory after the outbreak dubbed the Avalon cluster erupted to 70 commmunity based infections.

And people planning to travel to NSW to visit friends and family for Christmas have had their plans dashed.

Health authorities say the next 48 hours will be critical after the NSW government locked down the nothern beaches area until midnight on Wednesday and resurrected a small set of restrictions for Greater Sydney to contain the spread.

Former federal health department secretary and chair of the global Coalition of Epidemic Preparedness Jane Halton says NSW made the right choice to "go hard, go early, go household'.

But it could get worse before it gets better.

"If they discover it leaked into other places I have no doubt they will apply further restrictions and that is what they should do," Ms Halton told Nine's Today program on Monday.

"This is why they are asking people to be cautious to not go out, to limit the number of people and gatherings."

On Sunday NSW announced another 30 infections had been been detected as of 8pm Saturday night, which is the cut off time for daily infection counts.

Western Australia reimposed a hard border with NSW on Saturday.

People travelling from greater Sydney and the Central Coast will not be able to enter other states from Monday.

If they do, they will have to undergo 14 days of hotel quarantine in most states, or quarantine at home in South Australia and the ACT.

Only those from Greater Sydney will have to quarantine for two weeks on arrival in Tasmania.

Greater Sydney stretches from the Hawkesbury, Hornsby and the northern beaches regions in the north, to the Blue Mountains in the west, and the Wollondilly, Campbelltown and Sutherland regions in the south.

Travellers from the Wollongong local government area also cannot enter SA, while the NT, ACT, and Queensland have barred the entire Illawarra/Shoalhaven region.

There is a 24 hour grace period for Queensland and Victorian residents returning home, with authorities allowing them to quarantine inside their own houses.

Acting National Chief Medical Officer Paul Kelly on Sunday defended the way states and territories responded in restricting interstate travel.

"It's unfortunate that this is happening but we need to put safety and health concerns at the forefront," he said.

"Those on the northern beaches of Sydney, my heart goes out to you. This is a tricky time in the lead-up to Christmas but please stay the course."