UPDATE: Fire and health authorities in WA have both been placed on red alert as Perth braces for its hottest day in more than five years on Saturday.
Temperatures in the city are tipped to soar past 44C, with outlying metropolitan suburbs warned to expect even more intense heat over the weekend.
With catastrophic fire conditions to stretch from the Pilbara to the South West, bushfire brigades across the State have been told to prepare for the worst.
Department of Emergency Services deputy commissioner Lloyd Bailey said the forecast conditions were “significant and challenging” and fire crews would focus on the most at-risk areas south of the Pilbara in the Perth Hills and South West.
"This is really the first real hot couple of days that we’ve had and it extends such a broad area of the State, which obviously is a concern when we’re trying to move resources around,” he said.
Mr Bailey said fires that started in the morning were the biggest concern because conditions usually eased by the evening.
In Perth tomorrow night, the temperature is expected to remain at about 27C until Sunday.
“We’ve got quite a big window and a high-risk period,” Mr Bailey said.
"Volunteer firefighters have been rostered on all weekend, and extra water bombers have been placed on stand-by.
"We ask people not to just lock themselves up with the air-conditioning, but be cognisant of what is going on around them."
The Bureau of Meteorology’s Mike Bergin said hot conditions that had plagued the Pilbara in the past week were scheduled to extend to the South West this weekend.
“It’s a combination of the heat that’s in the North West that’s coming out of the Pilbara, basically that airs tracking to the south,” Mr Bergin said.
The elderly, those with young children and babies and tourists who might not be used to the heat have been particularly warned of the potential effects of the heat.
Health Department State health co-ordinator Revle Bangor-Jones said emergency departments were well aware of the need for extra staff in such hot conditions and would be preparing for a surge in presentations due to the heat.
The amount of staff would be determined by individual hospitals, she said.
"Although we are used to the heat, it is very important not to become complacent," Dr Bangor-Jones said.
"It is very important to keep the hydration levels up, and recognise any signs in the body that you are overheating."
Symptoms include dry, red, hot skin, high body temperature, nausea, and rapid heart rate.
St John's Ambulance advised anyone suffering from heat stroke should have cold packs or wrapped ice applied to their neck, groin and armpits, or be covered with a wet sheet while emergency services arrive.
In anticipation of the scorching heat, the scheduled race meeting at Ascot in the city has been postponed until Sunday.
Beachgoers are urged to stay alert and safe in the water this weekend.
The Department of Fisheries has warned people to keep an eye on Surf Life Saving WA's Twitter feed for postings about shark sightings.
Shark Response Unit spokesman Tony Cappelluti said helicopter patrols over Perth and South West beaches would continue, but people also needed to report shark sightings to protect the community.
"Judging by the regular flow of postings on the SLSWA Twitter service, lots of people have been reporting shark sightings and we encourage everyone to continue to help by alerting authorities," Mr Cappelluti said.
Mr Cappelluti said Rottnest would be popular with holidaymakers this weekend and, given a couple of reports of large white sharks near the island this week, people should keep an eye on the sighting and tagged shark detection alerts.
Anyone who sights a shark should call Water Police on 9442 8600.
Perth Zoo distributed monster icy poles to its animals as the heatwave gripped the city, with even the otters enjoying icy poles made from whitebait, blue bait, prawns and mussels.
Even fortunate pool and spa owners were being warned to take precautions, with a reminder to ensure water was properly treated so swimmers avoid catching amoebic meningitis, which thrives in water temperatures between 28 and 40 degrees.
The scorching temperatures will arise as a pocket of very hot air, which has subjected the Pilbara to intense heat this week, begins to move south.
Onslow has suffered through two successive days over 40C, with Paraburdoo topping 40C by 9.30am on Friday.
Mike Burgin, regional director from the Bureau of Meteorology, said Saturday was likely to be Perth's hottest day since Boxing Day, 2007.
"And Perth certainly won't be the worst of it. To the north-east of the city we will get temperatures up to 46C, 47C," he said.
The Department of Parks and Wildlife advises that some parks and recreation sites will be closed this weekend because of the heat.
People are urged to avoid these areas, follow the advice of Parks and Wildlife staff and observe signage.
People already in the area should leave for a safer place.
Closures on both Saturday and Sunday:
Perth metropolitan area and surrounding areas:
Lane Poole Reserve
Avon Valley National Park
Serpentine National Park
Walyunga National Park
John Forrest National Park
Greenmount National Park
Mundy Regional Park
Statham and Boya quarries
Gnangara and Pinjar off-road vehicle areas
Kennedy Range National Park
Mt Augustus National Park
Closures on Sunday only:
Wellington National Park - Honeymoon Pool and recreation sites on Lennard Drive
Hoffman Mill campground