A woman is in a critical condition after she suffered heatstroke while working at a Gold Coast market.
The 45-year-old collapsed at the Night Quarter precinct at Helensvale at about 4pm on Saturday, while another two people were hospitalised with heat-related illnesses.
Queensland Ambulance Service senior operations supervisor Luke Wyatt said she was in cardiac arrest when paramedics arrived, before being treated on scene and taken to the Gold Coast University Hospital in a critical condition.
Mr Wyatt said it appeared she had been working at the market throughout the day, with reports she was in a shed-like area.
"Anything that results in a confined area results in an elevated temperature," he said.
Mr Wyatt said it was an extreme case of heatstroke and urged other Queenslanders to be mindful of this weekend's hot conditions.
Heat exhaustion causes people to sweat, feel thirsty, lethargic and possibly nauseous.
Mr Wyatt said heatstroke was much more serious and needed "time-critical" treatment.
"Their thirst has gone, they're very dry to touch, they may have an altered level of consciousness, (be) confused, they can slip into having seizures and unconsciousness," he said.
"That can result in neurological damage, damage to the kidneys and it is a significant and dangerous event."
- Father shares horrific messages from daughter's bullies just days after Dolly Everett's funeral
- H&M stores trashed in protest over 'racist' hoodie
- Search intensifies for NSW man, 22, missing since New Year's Eve
The QAS has urged people to keep a lookout for children, the elderly and those doing manual labour in the sweltering weather.
Mr Wyatt said paramedics had been busy and received several call-outs for people with heat-related symptoms, as the temperature climbed towards a predicted top of 38C in Brisbane on Sunday.
Bureau of Meteorology forecaster Lauren Murphy said a southeasterly change would bring cooler temperatures in the late afternoon.
"There is some relief in sight," she told AAP on Sunday.
Ms Murphy said the predicted top of 38C was eight degrees above average for Brisbane in January.
"It's unusual but it's certainly not unprecedented," she said, referring to the city's record temperature of 43.2C.
But some records were broken in other parts of the state overnight.
Residents from the outback town of Winton endured their hottest ever overnight temperature on Saturday night, with the mercury dipping to just 33.1C.
Cloncurry also equalled its all-time warmest night with a low of 32.7C, while Longreach had its hottest night on record since 1902 with a minimum of 31.8C.