More than 500 children and pets were freed from locked cars in South Australia last year, the figures coming as the state swelters through a heatwave.
The Royal Automobile Association has called on people to take extra care over the next few days, with temperatures forecast to hit the mid-40s in some regional centres.
RAA Senior Manager Charles Mountain said cars could quickly heat up to more than double the outside temperature.
"Don't be tempted under any circumstances to leave children or animals unattended in a parked vehicle, especially not in this weather," Mr Mountain said.
"During heat waves like the one we're experiencing this week, the temperature inside a locked car will climb to dangerous levels within minutes."
The RAA said its service data showed 284 children and 230 pets were freed from locked cars last year.
It said a recent experiment it conducted showed in-car temperatures could rise to more than 80 degrees in 20 minutes in full sun.
Just a few minutes of exposure to this kind of heat can cause significant harm to a child, Mr Mountain said.
After two days in the mid-30s, the Bureau of Meteorology has forecast the mercury to hit 38C in Adelaide on Wednesday, 40C on Thursday and 39C on Friday ahead of a cool change.
That will make it the longest string of days of 35C or more since December 2019.
The conditions have prompted authorities to activate heatwave emergency plans, with the State Emergency Service urging people in the hottest regions to stay indoors if possible.
Community centres in Adelaide have been opened for rough sleepers and homelessness services are conducting outreach programs around the city.
The Red Cross will also provide free healthcare checks by phone.
Human Services Minister Nat Cook said South Australians were lucky to live in a community that looked out for and supported the vulnerable, isolated and elderly.
"This is the first significant heatwave in more than three years and it's critical that people stay safe," she said.
"Extreme heat during days is bad but, when it doesn't cool down overnight, people's bodies don't get a chance to recover and they can be at risk."
