Environment Canada has issued a heat warning for the city of Toronto, with several days of scorching temperatures in the forecast.

According to the federal weather agency, the hot and humid conditions arrived overnight and will linger until Wednesday.

Temperatures are expected to reach up to 32 C, with humidex values making it feel more like 40. Overnight temperatures will remain in the low 20s, providing little relief from the heat.

Prompted by Environment Canada's forecast, Toronto's chief medical officer has also issued a heat warning for the city. It will remain in effect until further notice.

"In addition to swimming pools, beaches and air-conditioned shopping malls, Toronto has 180 air-conditioned community centres and local libraries in neighbourhoods across the city," Dr. Eileen de Villa said in a statement, adding that the public can also make use of the city's seven cooling centres.

Monday and Tuesday will be so hot that transit will likely be affected, according to a spokesperson for Metrolinx.

Chance of slow orders is high during this late summer heat wave. Always travel with water. Give yourself a few extra minutes. There may be extra crowding as well as people squeeze in last minute fun & students arrive. Stay safe <a href="https://t.co/bnEIhikso0">pic.twitter.com/bnEIhikso0</a> —@femwriter

Environment Canada is reminding residents to stay well-hydrated by drinking lots of water and to never to leave people or pets inside parked vehicles. Children, pregnant women, older adults, people with chronic illnesses and people working or exercising outdoors are particularly at risk.