Western Australia's Department of Health is urging people to stay out of the heat as Perth's high temperatures continue.
The Bureau of Meteorology has forecast maximum temperatures of more than 40 degrees every day until New Year's Day.
Two people have been admitted to hospital for heat-related illnesses over the past few days.
State Health Coordinator Dr Tarun Weeramanthri says children, the elderly and those with chronic medical conditions are the most prone to heat stress.
He says symptoms could range from nausea and headaches to serious conditions including heat stroke.
"Stay indoors during the heat of the day if you can," he said.
"Stay cool - use the air conditioner if you've got one. Keep the house well ventilated.
"Drink plenty of fluids and avoid over-consuming alcohol or caffeinated drinks."
© ABC 2012
11:20 EST Since the the royals stepped off the plane on Wednesday afternoon, Sydney has turned on the great weather.