West Australian officials have failed to explain the cause of a hotel quarantine breach which has plunged millions of people into lockdown, despite acknowledging they provided incorrect advice about a security guard's actions.
The state has recorded three straight days of no new COVID-19 cases as it passes the halfway point of a five-day lockdown.
More than 12,300 tests were conducted on Tuesday, lifting the total over the past three days beyond 30,000.
The surge in testing, prompted by a hotel security guard who roamed the streets of Perth while infectious, paves the way for metropolitan Perth, the Peel region and South West to likely emerge from lockdown at 6pm on Friday.
"This is a very encouraging result, especially considering we are testing at record levels. But we are not out of the woods yet," Premier Mark McGowan said on Wednesday.
"I want the WA community to understand that if we do continue on a zero-case streak through to Friday, the lockdown will end ... but some form of restrictions will be necessary for the following week or so."
The government has announced anyone working in a "high-risk situation" in the quarantine hotels will now be required to wear a face mask at all times.
Health experts had expressed disbelief that such a policy was not already in effect.
And for the second time in as many days, officials were forced to clarify incorrect information they had provided about the breach.
Health Minister Roger Cook revealed the guard had not in fact delivered medication to a sick guest who is believed to have passed on the highly contagious UK strain of the virus.
He said the guard had been stationed in 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, during his shift at the Sheraton Four Points on January 24.
The guest received seven visits that day from guards and other staff wearing protective equipment, who dropped off food, medication and flowers.
None were from the guard who tested positive, a university student in his 20s dubbed "case 903".
"He has not told us, nor is there any information to suggest, he has gone into the room," Police Commissioner Chris Dawson said.
"I can also confirm there is no CCTV on that floor and in that respect, we can't corroborate as we normally do. But I again stress, this is not a criminal investigation."
Authorities are now examining whether the sick guest somehow transmitted the virus without face-to-face contact, either by airborne transmission or surface contamination.
"It's a working hypothesis. We haven't really nailed it yet," WA Health infectious disease expert Paul Armstrong said.
"We are dealing with a virus here that is changing ... we don't know whether the higher transmissibility of this (strain of the) virus is caused by it being able to be transmitted by air but we just have to be open to all options."
Contact tracers have identified 189 close contacts, 138 of whom have returned negative results.
Of a further 234 casual contacts, 116 have so far tested negative.
Mr McGowan said the guard's three housemates, who are in hotel quarantine, have been re-tested and their results are pending.
The guard's family has told The West Australian newspaper he has no serious symptoms but is distraught about having potentially infected others.
Fifty-four guests at the Sheraton who were due to finish their quarantine periods were held back so they could be re-tested as a precaution.
They have since returned negative tests and will be released later on Wednesday.
Opposition Leader Zak Kirkup slammed the government's management of the hotel quarantine system, accusing officials of complacency.
"We have a five-day lockdown because the hotel quarantine system failed," he said.
Authorities are yet to reveal what restrictions might remain in place beyond the lockdown, although schools are expected to return next Monday.