School children have been left without air-conditioning, tradespeople have been sent home, trains have been slowed and people have been asked to limit their electricity use as temperatures in south-west WA soar during a hotter than expected summer heatwave.

The temperature has reached 42 degrees Celsius in some parts of Perth on Wednesday afternoon, which is three degrees more than the forecast 39 C.

Extreme to severe intensity heatwave conditions have been forecast over parts of western WA, including Perth for the next three days.

Students at Bob Hawke College in Subiaco were confined to their classrooms at lunchtime and concerned parents told to collect them after a power failure left the school without air-conditioning, internet or landlines.

School principal John Burke said in an email to parents “all students are safe and in their classrooms, and have access to functioning toilets and water fountains, and can remain at the school until the end of the school day.”

“Should you wish to collect your child from the school due to the weather conditions or for any other reason, you may do so,” he said.

“The Department of Education is supporting the school to urgently rectify this situation.

“I will be communicating with parents later today to provide an update in relation to plans for tomorrow.”

Power usage warnings

In another email sent to all electricity owners, Synergy suggested people “switch off unnecessary appliances and limit your electricity use between 5pm and 9pm.”

“If you are using an air conditioner, set it to 24 degrees, which still feels cold when it’s hot outside,” the email read.