Perth has been plunged into a five-day lockdown after a confirmed case of Covid-19 went to various locations the community.
WA Premier Mark McGowan held an emergency press conference on Sunday afternoon, saying a male security guard aged in his 20s had been working at Sheraton Four Points in the CBD where there were four active cases, including two of the UK variant and one of the South African mutant strain.
He had tested negative on January 15, 17 and 23 but developed symptoms on Thursday.
"Exactly how the infection was acquired remains under investigation," McGowan said.
The lockdown applies to the Perth, Peel and South West regions and begins at 6pm WST on Sunday, running until 6pm on Friday.
"People in the Perth, Peel and South West regions need to stay inside their region for the next five days, unless for an essential reason," he said.
"We are strongly encouraging that everyone in this area who is from another WA region, stay here.
"Do not travel further outside of this area until the lockdown is over.
"If you do need to travel outside the region you are in now, that can only occur if you need to return to your place of residence."
Pubs, bars and clubs, gyms, indoor sporting venues, playgrounds, skate parks, outdoor recreational facilities, places of worship, libraries and the Crown casino are among venues that must close.
Restaurants and cafes can provide takeaway service only and just 10 people can attend funerals.
Weddings are cancelled.
No visitors are permitted to homes unless caring for someone vulnerable or in an emergency and no visitors will be allowed into aged care homes and hospitals unless there are exceptional circumstances.
School was due to start on Monday but that has now been put on hold.