TORONTO — There are heat warnings up across much of southern Ontario, spanning from Windsor to Ottawa and up to the Bruce Peninsula.

Environment Canada says temperatures could reach 33 C in some regions, while humidex values could be as high as 42.

At night, lows are only expected to hit between 20 and 22 C.

Environment Canada says the heat is expected to continue through Thursday.

It says the high temperatures could also lead to degrading air quality, which could affect people's health.

The agency says the risks are greater for young children, pregnant people, older adults, people with chronic illnesses and those working or exercising outdoors.