The Far West Local Health District is urging people to take the risk of heat-related illness seriously with temperatures expected to stay above 40 degrees for the next seven days.
Population health director Therese Jones says elderly people, babies, children, people with a medical condition and people who live alone are the most vulnerable.
She has some tips to keep cool.
"Drink plenty of fluid, consider other people who might be vulnerable and may not be able to look after themselves, stay in air-conditioning if they've got it, cool off in other ways like sponging down, going to an air-conditioned place," she said.
Signs of health-related illness include confusion, dizziness, fainting, nausea, vomiting, weakness, headaches and loss of sweating.
The Rural Fire Service is warning property owners to be prepared for the hot weather.
Inspector Bill Britt says brigades are on alert for possible fires and volunteers are being told they might be called up.
But he says landholders also need to be ready.
"Make sure they've got a tank full of water, the pump works, the hoses all work so that, should a fire break out, they've got some way of trying to hit it quickly before it takes off all hell breaks loose," he said.
Mr Britt says property owners need to put in fire breaks and have firefighting gear ready and that people should not do any grinding or welding.
The RSPCA is reminding people not to leave dogs in cars during this week's extreme weather.
Broken Hill shelter manager Merridy Wall says dog owners should make sure to provide their pets with plenty of water and shade.
"Definitely don't take them out in the cars. Even if you're only going to be five minutes into a shop, definitely don't do that," she said.
"It gets really hot in a car, so it can only take a couple of minutes and the dog can be in serious trouble."
Despite the heat, there's still work to be done on Mick O'Connor's sheep station near Milparinka.
He will be out making sure the sheep have access to water and do not walk into dams and get bogged.
"You just try and get away from the heat in the middle of the day and go early and use that time and then after five or six in the afternoon you've got a few hours you can use before it gets dark without knocking yourself around too much," he said.
© ABC 2013
07:25 EST Fog has been blanketing parts of southeastern Australia this morning, including the Adelaide and Canberra areas, affecting road and air traffic.