Another storm batters Mandurah | PHOTOS

Authorities received almost 180 calls for help after a cold front brought heavy rains and destructive wind gusts to much of the state's south.

Train services were disrupted on Tuesday morning after a tree branch brought down an overhead power line on the Armadale line and Mandurah trains were also delayed.

Power was gradually being restored to more than 21,000 homes and businesses, as far south as Lakelands.

"The damaging and destructive winds associated with the front have thrown debris, including tree branches, into the network damaging equipment," Western Power said.

"Our priority during the storm is responding to reported hazards to ensure the safety of the community and our crews. Repair work will be undertaken when safe, as some of the equipment needed ... cannot be used during dangerous winds."

Wind gusts of 135 km/h were recorded overnight at Cape Leeuwin and 124 km/h at Busselton Jetty, the Bureau of Meteorology said.

The strongest gust in Mandurah was 98 km/h.

People driving to work are being urged to keep their headlights on and be vigilant for fallen trees, branches and powerlines.

It is the third major storm front in what has already been the wettest July recorded in Mandurah in more than 20 years.

Another is expected to arrive on Thursday, potentially causing rivers to flood in the Perth Hills and the southwest including Mandurah.