The extreme weather event, typically seen only once every five years, is bringing wind gusts of up to 125 km/h to Perth and communities along Western Australia's coast.
Images of widespread destruction have flooded social media, including one showing a shed seemingly tossed into a swimming pool in Mandurah on the southwest coast.
"Act now and stay safe, with damaging to destructive winds expected this afternoon and evening," WA's Department of Fire and Emergency Services said in an alert issued on Sunday afternoon.
"Rarely experienced winds may bring down trees, branches and powerlines and loose items or debris may become airborne."
There were about 130 power outages recorded in multiple parts of Perth and its surrounds, with 14,600 customers affected statewide, according to Western Power.
Wind gusts of 117 km/h were recorded at Cape Leeuwin in the morning, while 104km/h gusts were marked at Cape Naturaliste.
The deep low pressure system brought high tides and eight-metre waves while flooding in Perth's CBD stranded cars and submerged walkways.
Residents had been urged to close their curtains and remain inside away from windows as the system approached the state's southwest in the morning.
"People should definitely tie down loose items like outdoor furniture and trampolines," Bureau of Meteorology duty forecaster Luke Huntington told AAP.
"When those strong winds are coming through, make sure you stay inside and just stay off the roads, in case of fallen power lines or trees."
Football fans attending the West Coast Eagles versus Essendon match at Optus Stadium were also been urged to plan ahead.
"This situation definitely doesn't happen every year and the wind is going to be the worst hazard," Mr Huntington said.
A major police search earlier wrapped up when an 11-year-old autistic, non-verbal boy was found safe after going missing overnight in Perth's western suburbs during the wild weather.
The boy had been missing for almost eight hours with police and State Emergency Service volunteers on foot and on horseback helping to locate him.
Several WA towns recorded heavy rain as the weather system moved through, with Ludlow, about 200km south of Perth, copping 43mm in two hours on Saturday night.
The cold front and low-pressure systems are expected to sweep across western parts of SA during Monday bringing rain and wind gusts of up to 100km/h before moving across the Adelaide region later in the day.
Severe weather warnings have been issued for SA's coastal regions, the mid-north and the southeast.
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