Thousands of Perth homes are without electricity this morning after rain and humidity combined to spark power pole fires.

Key points: About 100 power poles across Perth were damaged overnight, prompting blackouts

About 100 power poles across Perth were damaged overnight, prompting blackouts One Middle Swan school told parents to keep children home after losing all power

One Middle Swan school told parents to keep children home after losing all power After another cool day tomorrow, Perth temperatures will again heat up next week

Western Power said at its peak about 50,000 homes and businesses were affected by the blackouts overnight, with about 20,000 households still without power this morning.

By this afternoon power had been restored to all but 13,500 homes.

The utility's spokeswoman, Mitzi Vance, said the outages were caused by pole damage from a weather front that passed through the Perth metro area overnight.

"With the humidity and the light rain overnight, because of the hot weather and the dust build-up on our poles, they have just reacted and damaged a number of our poles around various locations in the metro area," she said.

Humid conditions or light rain can combine with dust and pollution and create paths or "tracks" on the insulators, allowing electricity to jump across.

About 100 poles were damaged in various locations overnight, with about 50 pole top fires recorded.

About 23,000 properties had supplies restored overnight by back-feeding power around the damaged sections of the network.

School tells students to stay home

Swan Christian College sent a message out to parents to keep children home today given there was no certainty about when power would be restored to its campus in Middle Swan.

Thousands of homes had power restored overnight but many others remained offline this morning. ( Supplied: Western Power )

"Due to a complete power outage at the college with unknown restoration time, parents are asked to keep all students at home today," the school said in a Facebook post.

"Students who are already on their way via public transport will be supervised at the college until they can be picked up by parents (as soon as possible please).

"We apologise for any inconveniences caused and will keep you updated as soon as we hear from Western Power."

Main Roads WA warned motorists to be wary of traffic signals blacked out in various suburbs throughout the metropolitan area and about power poles being down in some areas.

Bureau of Meteorology duty forecaster Steph Bond said Perth received 1.2 millimetres of rain on Wednesday night and could expect a few more showers on Thursday morning.

Another cool day was expected on Friday, with a top of 24 degrees Celsius.

But the weather was expected to heat up again next week, with temperatures returning to the mid-30s on Sunday and increasing to the high 30s next week.

Western Power has encouraged people affected to check its outages map for estimated restoration times.

Perth forecast