On Friday, Metropolitan Perth and the Peel region entered a snap three-day lockdown after a hotel quarantine outbreak led to community transmission.
The premier said lockdown was a necessary measure after two people, including a man who stayed in the hotel and completed quarantine before flying to Melbourne, spent days in the community while infectious.
Anzac Day dawn services have been cancelled and people in the affected regions must wear masks when leaving their home.
"I know this is hard to take and I wish we didn't need to be doing this," he told reporters on Friday.
"But we can't take any chances with the virus. We just can't."
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Genomic testing has confirmed the virus spread in the corridors of the Mercure Hotel Perth from a couple who had returned from India.
A pregnant mother and her four-year-old daughter who were staying across the corridor tested positive and remain in quarantine at the hotel.
A man who was staying in the room adjacent to the couple has also tested positive. The man, who is asymptomatic, arrived in Melbourne on Wednesday after completing 14 days of quarantine at the hotel. His five-day visit in Perth after he left quarantine has led to two community cases - a female friend he stayed with and a man who dined near the pair at a restaurant.
On Thursday, the premier announced the Mercure Hotel, which is one of three Perth quarantine hotels deemed to be of "high-risk" for ventilation issues, would no longer accommodate returned overseas travellers.
It will instead transition to a "low-risk" quarantine hotel for a flight-load of seasonal workers expected to arrive from Tonga and Vanuatu next month.
In light of the outbreak, states and territories have taken precautions against travellers from Perth and Peel. New Zealand, which just opened a trans-Tasman travel bubble with Australia last week, also announced a pause on travel from Western Australia.