A late-summer blast of hot weather has prompted Environment Canada to issue a heat warning for Toronto.

The weather agency is forecasting a high of 30 C on Tuesday, though the humidity will it make it feel like the temperature outside is closer to 40 C.

Environment Canada says it won't last long, as an incoming cold front will bring the temperature down from Tuesday night onward.

According to Environment Canada, the people most at risk during periods of extreme heat include infants and children, the elderly and those with chronic health conditions.

Anyone working outside or exercising can also find themselves at risk, along with those without access to air conditioning, including homeless residents.

The heat warning was issued on Monday afternoon, on a day in which the mercury went up to 27 C in the city.