Passengers flying into Perth from Adelaide on Sunday received a shock on landing after being told to either adhere to strict new coronavirus measures or fly back home.

Western Australia immediately imposed new coronavirus measures for South Australia after an emergency meeting between WA’s police commisisoner, premier and chief health officer on Sunday. It comes less than 48 hours after the state lifted its tough border restrictions and is a direct response from a growing cluster of coronavirus cases in South Australia announced just hours earlier.

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Any one arriving in Perth from South Australia will now need to be tested for COVID-19 and must self quarantine for 14 days. The new measures for South Australia equal those required for New South Wales and Victoria.

So abrupt were the new measures, one Qantas flight was mid-air when the measures were introduced and passengers were given the news from health officials at the airport upon landing.

Meanwhile, passengers waiting for another flight from Adelaide to Perth at the airport were notified before departur and were given the option to disembark.

South Australia recorded its first community transmitted coronavirus cases since April – seven months – after three infections were reported on Sunday.

The source of the new infections are not known with health authorities fearing hundreds of people in the city’s northern suburbs could have been exposed to the deadly virus.

The next 24-hours will be crucial in identifying the source of the “potentially disastrous” outbreak.

It is understood Qantas gave passengers the option to return to Adelaide and a number have indicated they will take the option and fly back on Monday.

It was a dramatic turn of events for the airline which turned 100 overnight.

Under the new rules, anyone arriving from South Australia at Perth Airport will now be tested for COVID-19 on arrival (or within 24 hours of arrival at another COVID clinic) and on quarantine day 11.

Arrivals must self-quarantine “in a suitable premise” for 14 days.

“These are initial steps the State Government is taking to protect all Western Australians, and will be reviewed regularly,” a statement read.

“We will monitor the position in South Australia very closely and will strengthen measures if required.

“We understand these changes will cause frustration for many people, but these steps are being taken on the best health advice to protect everyone.”

A woman in her 80s was diagnosed at Adelaide’s Lyell McEwin Hospital emergency department on Saturday after visiting on Friday night, leading to 90 staff and patients being ordered to quarantine.

Two of the woman’s family members, a female in her 50s and a man in his 60s, have tested positive for the deadly virus.

The three are all from the same family and are related to a staff member from a medi-hotel holding quarantined patients in Adelaide. Health authorities say they are considering this as the likely source but the information is “very, very early”.

Four other members of the family are showing symptoms and are awaiting coronavirus testing results.

The state’s chief health officer Professor Nicola Spurrier described the new cases as “very troubling”, revealing the woman had visited a suburban shopping centre, Parafield Plaza Supermarket.

She said the cluster is the worst outbreak in South Australia yet, fearing multiple public venues may have been visited by family members yet to be confirmed as infected patients.

“I’m expecting that we will have more cases,” Prof Spurrier said Sunday.