Swathes of Western Australia have completed their first night of lockdown, triggered after a hotel quarantine security guard attended more than a dozen venues while infected with COVID-19.

The snap lockdown decision has tested the state’s contact tracing capabilities as hundreds of people formed queues outside clinics in affected regions.

The WA government granted an extended trading permit overnight to several Coles stores after thousands flocked to the major supermarket chains and shopping centres to stock up on supplies despite authorities urging people not to panic buy.

The confirmed case has ended WA’s 10-month streak of no locally acquired infections.

From 6pm on Sunday, almost two million people in metropolitan Perth, the Peel region and the South West region entered lockdown, which will last until 6pm on Friday.

Overnight, a second suspected case presented to Fiona Stanley Hospital and is awaiting results but the Health Department says the case could be historic.

“Western Australians have done so well for so long, but … this is a very serious situation and each and every one of us has to do everything we personally can to stop the spread in the community,” Premier Mark McGowan said.

“I know for many Western Australians this is going to come as a shock,” he said.

Long queues outside the Royal Perth Hospital Covid-19 Clinic late into Sunday night. Photo: Getty

The lockdown means all residents must stay at home unless shopping for essentials, attending to medical or healthcare needs, exercising within their neighbourhood or working if unable to do so remotely.

Schools which were due to resume on Monday will remain closed for another week.

Authorities believe the man in his 20s, who worked at the Sheraton Four Points hotel in Perth’s CBD, has probably contracted the highly contagious UK variant of the virus and have urged anyone to get tested if they have symptoms.

Perth hotel Four Points by Sheraton is the epicentre of the lockdown. Photo: Getty

Mr McGowan said the Maylands man returned a positive test overnight on Saturday after last working at the hotel on January 27. He first experienced symptoms a day after.

He returned three negative tests between January 15 and 23 and it is believed he was probably first infectious from January 26.

The man had worked two 12-hour shifts on January 26 and 27 on the same floor as a person infected with the highly contagious UK variant of the virus.

Genomic testing confirming the source of his infection will not be available until Tuesday morning.

His three housemates have tested negative but have been placed into hotel quarantine for 14 days. Any other close contacts will also be required to isolate.

WA Health released a list of 15 venues, mostly in Maylands but also included the Perth Convention Centre and a GP practice in Nedlands, that the man attended between January 25 and January 30.

Hundreds of people began queuing at testing stations almost immediately the list was released, knowing they had been in or near those specific locations.

Authorities are investigating the breach but say the guard did not enter a hotel room.

Chief Health Officer Andy Robertson was unable to judge whether there was likely to have been community spread.

“We do get super-spreaders within COVID-19,” he said.

“But we’ve also had others like the 20-year-old lady in Queensland who was out in the community for three or four days and didn’t manage to spread it to anybody.”

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Long queues formed at Perth supermarkets when word spread that a significant announcement would be made.

Mr McGowan urged the community not to panic-buy groceries, saying the state was well equipped to ensure supplies.

Other states moved quick to close borders or restrict travel.

South Australia slammed its border shut to all of WA on Sunday night.

Victoria, Queensland, Northern Territory and Tasmania restricted travel from the locked-down areas of WA.

People travelling to NSW from the affected areas must take a COVID-19 test and stay at home.