New South Wales’ ‘lockdown lite’ approach to containing its coronavirus outbreak is putting the nation in jeopardy, some of Australia’s leading epidemiologists have warned.

On Friday, Sydney’s northern beaches COVID-19 outbreak grew to 28 cases and each state and territory imposed new restrictions for people who have recently been or were planning to travel to the area. 

NSW health authorities remain concerned they have not yet found patient zero and therefore don’t know how widespread the outbreak is.

To stop the virus spreading any further the NSW government has asked Northern Beaches residents not to leave their homes. 

On Friday evening, NSW Health issued an “urgent call to all residents of NSW – not only those in the Northern Beaches – to monitor for COVID-19 symptoms”.

Cars line up for COVID testing in Bondi Beach on Friday. Photo: Phoebe Ashton

“Anyone in the state with even the mildest symptoms such as headache, fatigue, cough, sore throat or runny nose, is asked to come forward immediately for testing, then isolate until a negative result is received,” NSW Health said.

“The source of these infections remains under investigation, though genome sequencing points to the strain being of US origin.”

But leading epidemiologists say the state needs to heed Victoria’s lessons by implementing a hard lockdown for the 270,000 residents of the affected area, and mandatory mask wearing for the rest of Sydney.

This needs a hard lockdown. The concern is high,” University of Melbourne epidemiologist Tony Blakely said.

“Masks should be on everybody, they’re cheap, they don’t have a big cost, they work. And what it means is if the virus pops up in Western Sydney for instance, its chance of spreading is far less.”

The timing of the outbreak couldn’t be worse, with Christmas just a few days away and many Australians preparing to fly across the country to see loved ones.

“What we have is a state that has been successful in relying on contact tracing and they’ve done well, but they haven’t been tested,” said Professor Blakely.

“This is the test. It’s explosive and right before Christmas. It’s time to dig deeper into the toolbox.”

Gladys Berejiklian has urged Northern Beaches residents to stay home. Photo: Getty

Australia knows enough about the virus and how to handle it now to stay on top of an outbreak, Professor Blakely said, but the latest eruption puts the nation’s elimination of COVID at risk.

“I’m more worried about this busting up the elimination in all states and territories,” he said.

UNSW epidemiologist and World Health Organisation adviser Mary-Louise McLaws said Australia could expect to see more cases in NSW over the coming days.

“There will be more. We don’t know the source or the quarantine hotel, or flight crew,” Professor McLaws said.

Bringing people back without testing them at the airport is the weak link. We have to shore that up.”

When Victoria tried to fence off suburbs before the second stage four lockdown it failed dramatically, because there was no testing of people going in or out, Professor McLaws explained.

Imposing a stronger lockdown on the Northern Beaches could ward off a similar situation, she said.

Epidemiologists say Sydneysiders should be wearing masks. Photo: AAP

“When you’re dealing with a highly infectious disease in a highly mobile community during a festive season, the best approach is to be precautionary,” Professor McLaws said.

“We should learn from what has happened in Victoria.”

Deakin University chair of epidemiology Catherine Bennett said even if the management of flight crew was not related to the current outbreak, tightening it is still a good idea.

Rapid contact tracing is vital to containing the Northern Beaches cluster, Professor Bennett said.

“Testing response from the public is also strong, and together this will add an extra layer of protection until NSW Health can be sure that there are no more active cases associated with this cluster,” she said.