A coronavirus cluster in Sydney’s northern beaches that has surged to 17 cases has been sourced back to an international case, NSW Premier Gladys Berejiklian has confirmed.

It comes as holiday plans are in chaos as states moved quickly to slap restrictions on travel from Sydney’s northern beaches.

There are concerns state borders may be slammed shut over Christmas after the NSW outbreak grew from two cases on Wednesday to 17 late on Thursday.

The peninsula has entered a quasi-lockdown, with NSW Health asking residents to stay home and not leave the area for the next three days.

Queensland has announced anyone arriving from Sydney on Friday and who has been to the northern beaches since December 11, must get tested and self quarantine for 14 days.

Those measures will toughen further from 1am Saturday, when travellers from Sydney who have been to the region will be forced into hotel quarantine.

The West Australian government says anyone arriving from NSW will be required to self-quarantine for 14 days and get tested on day 11.

“I understand these changes will cause some frustration and uncertainty for some people,” WA premier Mark McGowan said.

People line up for Covid-19 testing at Mona Vale Hospital’s walk-in clinic in Sydney on Thursday. Photo: AAP

The Queensland government has banned anyone who has been in the NSW northern beaches region since December 11 from visiting aged care homes, hospitals or prisons in Queensland.

Tasmania has already moved to prevent people who visited high-risk locations in NSW from travelling there.

Northern Territory authorities said anyone from the northern beaches area travelling to the NT will need to undertake 14 days of mandatory, supervised quarantine in either Alice Springs or Darwin.

Victoria similarly told entrants to the state from the northern beaches that they must get tested and quarantine in their home or accommodation for 14 days from the date they left the northern beaches.

Meanwhile people in NSW are being urged not to travel to the northern beaches if they don’t have to.

Northern beaches residents have been told to keep to their household groups, and work from home if they can.

They have also been told to avoid unnecessary travel outside the region, and not to visit high-risk venues including clubs, restaurants, places of worship and gyms.

NSW broke its 12-day streak without locally acquired coronavirus cases on Wednesday. Photo: AAP

Health authorities are racing to stem the damage from the mystery coronavirus cluster, with residents of the peninsula entering a quasi-lockdown.

NSW Health has asked locals to stay home as much as possible and not leave the area for the next three days.

Two northern beaches cases were announced on Wednesday evening, with three more described by health authorities at a press conference on Thursday morning.

News of 12 further infections came on Thursday afternoon.

The source of the outbreak remains a mystery. Sewage testing last week uncovered no virus fragments in the area, indicating the virus was newly introduced to the northern beaches.

The Pittwater Palms facility is closed to visitors, while those in contact with the infected worker are being tested and are self-isolating.

NSW’s 12 consecutive days without a locally transmitted virus case ended on Wednesday after a Sydney airport driver tested positive and two cases popped up on the northern beaches – a woman in her 60s and a man in his 70s.

Health alerts have now been issued for a number of venues across Sydney’s northern beaches.

The development comes after interstate travel restrictions had been lifted.

-with AAP