Toronto has issued an extended heat warning for the city after days of scorching temperatures.

The city's medical officer of health, Dr. Eileen de Villa, upgraded the existing heat warning to an extended heat warning Wednesday morning based on information from Environment and Climate Change Canada.

The extended heat warning will be in effect until further notice, the city says.

Toronto will see a high of 30 C on Wednesday, with a humidex of 40. The forecast also calls for a 40 per cent chance of showers this afternoon, with the risk of a thunderstorm.

Environment Canada says that a cold front is expected to move through the area in the afternoon, which is expected to bring an end to the heat event.

Many at risk

During extended heat warnings, the city encourages the public to visit family, friends and neighbours to ensure that they are drinking enough liquids and are staying cool during the heat.

People at risk during the particularly warm weather include those with chronic illnesses, limited mobility or some mental health illnesses. Infants, young children, people on certain medications and the homeless may also be at risk.

Young children and infants may be particularly at risk during the extreme heat. (Mark Blinch/Reuters)

To stay cool, the city says that several swimming pools, beaches, malls, community centres, cooling centres and libraries will be available throughout the city. Several drop-in sites across Toronto will also have TTC tokens available for the homeless to allow them to get to cool places.

The city's cooling centres will have air-conditioned spaces for people to rest indoors as well as cool drinks and light snacks. Staff will also be on hand at the city's seven cooling centres to help those affected by the heat.

Landlords of buildings without air conditioning are encouraged to provide a similar cooling room to help residents get relief from the heat.

How to beat the heat

To stay cool during the extreme heat, the city says you can take precautions like drinking water even when you don't feel thirsty, going to air-conditioned spaces, and taking showers or baths. You can also wear loose clothing and hats, avoid the sun and reschedule events for cooler times during the day.

Toronto’s Metro Hall provides an air-conditioned refuge for those looking to escape the heat. (Timothy Neesam/CBC)

The city is also reminding people not to leave children, seniors or pets unattended in vehicles.

Air pollution typically increases when the weather becomes warmer, the city also says. It reminds those with heart and lung conditions, seniors and parents and guardians of young children to pay particular attention to the air quality health index levels and forecasts.