WA Health has issued a list of exposure sites after two truck drivers tested positive to COVID-19 while in Western Australia.
The drivers, aged 23 and 29, completed a routine COVID-19 screening test on August 25 before they left New South Wales.
They drove through Victoria and South Australia on their way to WA and slept in their truck and had minimal contact with other people.
They also wore masks when outside of their trucks.
On Friday, the drivers were told they had tested positive via text message from NSW Health and were immediately put into hotel quarantine with mild symptoms.
On Saturday, Premier Mark McGowan confirmed 20 people had been identified as close or casual contacts and they are in isolation.
Anyone who has visited an exposure site during the listed times must quarantine immediately for 14 days and get tested within 48 hours.
Exposure sites. PIC: HealthyWA website
Mandurah Crab Fest boasts huge range of free, family friendly entertainment
Fuel prices surge in Perth, Mandurah
Teen boys charged over Mandurah burglaries
Tragic update in search for missing man Robert Snyder
Premier Roger Cook to leave Kwinana electorate, move to Perth
Mandurah Marine Rescue's new vessel named in memory of nun who survived 1959 boating accident
Teen dies in motorbike crash at Waroona Dam
Shark alert issued after whale carcass reported at Preston Beach
Kwinana businesses to refuse serving students during school hours