Residents in South West Australia's Collie town are currently preparing for a severe flooding situation after a storm on Wednesday dumped more than 189mm of rainfall in just 24 hours.

The summer thunderstorms, labeled as a one-in-100-year phenomenon, forced residents to leave their properties. It eventually damaged 40 homes and businesses in Collie.

Attention is now being focused on Collie River as it could swell what with the large amount of rainfall that it received. Although authorities remained confident the Collie River won't break its banks, hundreds of sandbags are however needed to help prevent its water from spilling out into the town.

"The Collie River at Collie is currently below the minor flood level and steady but expected to rise. Based on recent and forecast rainfall moderate to major flooding is expected to develop around and downstream of Collie early Thursday morning," the Weather Bureau warned.

"We're expecting that this level of rain that we're getting now could continue for up to 12 hours," Jason Whiteaker, a local official, said. "So we've got a long night in front of us, I think."

Located 132 miles south of Perth and 37 miles inland on the Collie River, the town is normally hot and dry during the Australian summer.

According to the Weather Bureau, most of the heavy rainfall occurred during daylight hours on Wednesday. Yourdamung Lake received 189mm, Yourdamung Farm at 184mm and Collie at 133mm. The highest fall in the metropolitan area was registered at 50.6mm at Champion Lakes.

The thunderstorms have likewise left about 6,000 Perth residents without electricity.