A second suspected case has come forward in WA after a Perth hotel quarantine guard’s infection triggered a five-day lockdown of nearly 80 per cent of the state’s population.

Authorities are racing to determine how the 20-year-old guard contracted the virus after it was confirmed he did not enter a hotel room but did patrol the same floor as an infected guest in quarantine.

A second suspected case presented to Fiona Stanley Hospital and is awaiting results but the Health Department says the case could be historic.

The security guard’s infection triggered sudden five-day lockdown and compulsory mask-wearing in metropolitan Perth, the Peel region and the South West region, ending WA’s 10-month streak of no locally acquired cases.

Even before the emergency measure was announced on Sunday, the rumour mill sparked a wave of panic buying and supermarket shelves were stripped amid the premier’s pleas not to.

There were queues outside shops and people lined up for testing outside COVID clinics.

Waiting to get tested on Sunday night outside Royal Perth Hospital. Photo: AAP

More than two dozen federal WA politicians flying to Canberra for the resumption of parliament were caught up in the chaos and forced to isolate until Friday and stay away from Parliament House.

States reacted quickly with South Australia slamming its border shut and
Victoria, Queensland, Northern Territory and Tasmania declaring a hotspot.

West Australian Premier Mark McGowan said the five-day lockdown which started at 6pm Sunday was about moving early to save heartache down the track.

“It is as hard as anywhere, designed to try to crush the virus and stop it from getting a foothold in Western Australia,” he said.

“This will be very disruptive to many families and many businesses. But what we’re trying to do is have a period of disruption rather than a long period of disruption, and therefore some adverse health outcomes.”

All residents must stay at home unless shopping for essentials, attending to medical or healthcare needs, exercising within their neighbourhood or working if unable to do so remotely.

Schools which were due to resume on Monday will remain closed for another week.

Authorities believe the man in his 20s, who worked at the Sheraton Four Points hotel in Perth’s CBD, probably has the highly contagious UK variant of the virus.

Authorities are investigating the breach but say the guard did not enter a hotel room.

Mr McGowan said the Maylands man returned a positive test overnight on Saturday after last working at the hotel on January 27. He first experienced symptoms a day after.

He returned three negative tests between January 15 and 23 and it is believed he was probably first infectious from January 26.

The man had worked two 12-hour shifts on January 26 and 27 on the same floor as a person infected with the highly contagious UK variant of the virus.

Genomic testing confirming the source of his infection will not be available until Tuesday morning.

His three housemates have tested negative but have been placed into hotel quarantine for 14 days. Any other close contacts will also be required to isolate.

WA Health has released a list of 15 venues, mostly in Maylands but also including the Perth Convention Centre and a GP practice in Nedlands, that the man attended between January 25 and January 30.

Chief Health Officer Andy Robertson was unable to judge whether there was likely to have been community spread.

“We do get super-spreaders within COVID-19,” he said.

“But we’ve also had others like the 20-year-old lady in Queensland who was out in the community for three or four days and didn’t manage to spread it to anybody.”

–with AAP