Environment Canada has issued a heat warning for Friday and Saturday for most of southern Ontario and all of the Greater Toronto Area.
The weather agency is calling for daytime temperatures of 30 C or higher, with humidex values of 40 or higher.
Nighttime lows are expected to be in the low to mid 20s, Environment Canada said in its warning.
“Extreme heat affects everyone,” Environment Canada said, warning that people should not leave children or pets in parked vehicles.
Cooler air and less humid temperatures are predicted to arrive on Sunday.