Environment Canada says Monday's temperature is expected to reach 33 C in the city, and Tuesday's high is also forecast to reach at 33 C, before things start cooling off later in the week.
During an extreme heat alert, people are encouraged to check on family, friends and neighbours, especially vulnerable adults and children, to make sure they are keeping cool and drinking plenty of fluids.
People are also encouraged to seek shelter at air-conditioned shopping malls, libraries, community centres and city-run cooling centres in order to stay cool.
Other tips on coping with the heat include drinking lots of cool water, wearing loose, breathable clothing and a hat, staying in the shade and never leaving children, seniors or pets unattended in a car.
Officials say the extreme heat alert will be in effect until further notice.
The city first issued a heat alert on Sunday, as temperatures began to climb and eventually reached 32.1 C.
Environment Canada has issued a special weather statement for most of southern and eastern Ontario, warning of hot and humid air and high temperatures in the low 30s on Monday. Humidex values are expected to reach 40 in many areas.
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