A hotel quarantine security guard in Perth and two of his housemates have tested positive to coronavirus after he spent several days infectious in the community.
Premier Mark McGowan says health authorities will assess any further infections over the weekend before deciding whether the city returns to lockdown.
The man in his 20s, who worked at the Pan Pacific Hotel on April 24, 25 and 26, moved through the community between April 27 and 30 while potentially infectious.
After a routine weekly PCR test required of all hotel quarantine workers on Friday, he received a positive result on Saturday morning, prompting him and his seven housemates to be moved into hotel quarantine.
Two of the housemates have since tested positive - a roommate and a house guest from Canberra. The guard had recently received his first COVID vaccination.
Despite the new cases, the West Australian premier said a lockdown would not be called "at this point".
"But it is possible this could change by tomorrow or the day after," Mr McGowan told reporters on Saturday afternoon.
"This is an extremely difficult situation we are dealing with. We are effectively in a holding pattern."
He said health authorities had asked for time to conduct contact tracing on Saturday and overnight before deciding on the need for a lockdown.
The early detection of the cases, combined with WA's interim restrictions following a snap three-day lockdown last weekend, and ongoing mask wearing rules are the factors the justify holding off on another lockdown, the premier said.
Authorities are buoyed by the fact Perth and Peel residents have been moving less through the community during the guard's infectious period.
Mr McGowan said a slight relaxation of outdoor mask wearing rules as of midnight on Friday would be now be rewound.
All Perth and Peel residents must wear masks indoors and outdoors, regardless of proximity to others.
The security guard worked on the same floor as some confirmed cases at the Pan Pacific Hotel on April 24, but it is unclear how he became infected. He returned negative saliva tests on all three days he worked between April 24 and 26.
Both positive cases revealed in routine testing on April 24 stayed on the same floor the guard was working.
"CCTV vision is being reviewed, however there is no clear explanation at this point as to how this security guard could have been infected," Mr McGowan said.
The premier has given a rundown of the man's movements from April 27, when he was not at work and authorities suspect he may have been infectious, until entering hotel quarantine on Saturday.
On April 27, the man went to visit friends and on April 28, he went to Spudshed in Stirling, Northland shopping centre in Balcatta, Agha Juice Cafe in Joondanna and saw friends later that evening.
On April 29, he shopped at Coles in Northland Shopping Centre Balcatta and then met with friends. He developed some COVID-19 symptoms that evening, which he thought were related to his Pfizer vaccine days earlier.
On April 30, he visited Mirrabooka Mosque for 30 minutes then went to a hotel quarantine facility for his weekly PCR test. His positive result came through on Saturday morning.
The locations the guard visited are listed on the healthywa.wa.gov.au website as exposure sites.
Testing centres are ramping up to process those who may have been exposed to the guard.
Australian Associated Press