Western Australia's hotel quarantine rules will be further tightened as much of the state prepares to emerge from lockdown.
WA has posted a fourth consecutive day of no new community COVID-19 cases, paving the way for metropolitan Perth, the Peel region and South West to almost certainly conclude their lockdown at 6pm on Friday.
Two unrelated infections were recorded among overseas travellers in hotel quarantine, Premier Mark McGowan confirmed on Thursday.
More than 37,000 tests have been conducted over the course of the five-day lockdown.
"This is a remarkable achievement. I think it's a result that is a full credit to every person currently in lockdown and getting tested," Mr McGowan told reporters.
"Western Australia is in a strong position. We know that things can change in an instant and we need to stay the course."
The government is expected to announce as early as Thursday night what restrictions will remain in place beyond the lockdown.
"I need to stress that it will be a little longer before things go back to the way we've become used to," Mr McGowan said.
The streak of zero cases comes after a security guard at the Sheraton Four Points hotel unwittingly roamed the streets of Perth while infectious.
Authorities are continuing to investigate how he contracted the highly contagious UK strain of the virus from a sick guest.
His four closest contacts have been re-tested and all again returned negative results.
Anyone working in a "high-risk situation" in quarantine hotels must now wear a face mask at all times, a policy doctors were stunned did not already exist.
Health Minister Roger Cook on Thursday announced such workers will also be required to wear protective eyewear.
The government also plans to implement a recommendation from Victoria and introduce saliva tests between shifts for hotel quarantine workers.
Mr Cook said the potential transmission of the UK variant between rooms of a Melbourne quarantine hotel showed how challenging the new strain was.
"It's certainly the cause of the outbreak in Queensland, it's the cause of the outbreak in South Australia. We are no orphans on that," he said.
"So I think that means that we really do need to get new public health advice to really just make sure we nail down this one."
Mystery surrounds the viral transmission that prompted the Perth lockdown.
The guard had been stationed on a chair near a stairwell about three metres from the room of the guest, who had been "quite unwell" and remained in quarantine for three weeks.
The guest received seven visits on January 24 from guards and other staff wearing protective equipment, who dropped off food, medication and flowers.
But contrary to previous government advice, none of the visits were from the guard who tested positive, a university student in his 20s dubbed "case 903".
Authorities are now examining whether the sick guest somehow transmitted the virus without face-to-face contact, either by airborne transmission or surface contamination.
Authorities have identified almost 450 close and casual contacts of the guard and more than 350 have so far tested negative.
WA's planned re-categorisation of Victoria as "very low risk" has meanwhile been put on hold, meaning incoming travellers will still need to quarantine for 14 days.