Unseasonal wild weather is lashing much of WA's South West as residents in Rockingham and Mandurah, south of Perth, clean up after flooding overnight.
The SES received 100 calls for assistance after a thunderstorm dumped 70 millimetres of rain on Rockingham and Mandurah overnight.
It was the city's wettest December day on record.
Incident controller Steve Summerton says many suburbs had flash floods.
"Most of the callouts last night were related to flash flooding, where unfortunately the water comes down fairly fast, it rises and goes through doorways into households and disappears just as quick," he said.
"We've also had reports of some roof damage with water leaking in through blocked gutters etc."
Rockingham Hospital has sustained severe damage in the storm and there has been flooding in areas.
It has postponed some elective surgery and relocated patients within the hospital.
The Department of Agriculture in Harvey has recorded 109 millimetres of rain in the last 24 hours, a one-in-100 year occurrence.
The Weather Bureau's Neil Bennett says the intensity of the rain is likely to continue.
"It's not going anywhere in a hurry and it's highly likely that we're going to see further heavy falls and it wouldn't be out of the ordinary to see 50mm plus again in the next 24 hours, perhaps even locally heavier than that," he said.
In Cooloongup, local resident Roy was watching TV when the storm broke in the early hours of the morning.
"She just crackled wildly, humongous, and the whole power just went off and then about a couple of minutes later she started coming back slowly but then the rain came and that rain was just too much," he said.
"Flooded my back rumpus room, water coming down through everywhere right around the edge of the house and all my electricals, freezers, fridges and TVs," he said.
About 4,600 households, mostly in Mandurah, lost power.
Western Power reports that lightning struck some houses in the area and its crews are working to restore power to affected areas.
It says people who see fallen powerlines should stay clear and call the company straight away.
© ABC 2012
16:06 EST The weather bureau has implemented a new system of forecasting the seasonal outlook called Predictive Ocean Atmosphere Model for Australia, or POAMA.