Toronto's weather is a triple threat on Saturday as the city swelters under a heat alert, a humidex advisory and a smog advisory.

Toronto's medical officer of health announced the heat alert. Residents are reminded to call or visit people vulnerable to the heat, including seniors, young children, and people with pre-existing illnesses.

The smog advisory stretches from Windsor to Kingston. Environment Canada said a stagnant weather pattern will cause pollutants from the U.S. to accumulate and react with sunlight "to form photochemical smog." People are asked to avoid non-essential car trips and the use of gas-powered motors, oil-based paints and aerosol sprays.

Higher pollution levels are expected to disperse Sunday.

Environment Canada's humidex advisory stretches from Windsor to Ottawa, including the Bruce Peninsula and the Niagara region.

Environment Canada says people should stay in air-conditioned or shady areas, limit their activities and drink plenty of water.

An approaching cold front from the north on Sunday will bring relief from the high humidex values, the weather agency said.