A fifth fatality may also have been caused by the heat, they said.
In the USA, one woman reportedly died Saturday in Pennsylvania after going into cardiac arrest due to the heat, and a 30-year-old man collapsed while running a race in NY.
"The record temperatures are expected to continue in central and eastern Canada, so make sure you know how to protect yourself and your family", Trudeau said.
The number of heat-related deaths in Montreal was pegged at six on Tuesday.
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Heat warnings are issued when very high temperature or humidity conditions are expected to pose an elevated risk of heat illnesses, such as heat stroke or heat exhaustion.
People at risk of heat-related illnesses include those with chronic illnesses, people with limited mobility or certain mental health illnesses, infants and young children, people on certain medications, and the homeless.
At least eight people in the USA and Canada have died in the past week due to the intense heat wave affecting parts of North America. The last one was in 2011 at eight days.
An extended heat warning issued by the city's medical officer of health on Sunday remains in effect.
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"The children will be supplied with food that could last at least four months", BBC quoted Thai military as saying. Several fissures have been found and teams have explored some, though so far none have led to the trapped boys.
The move is part of the federal government's climate change adaptation in expectation of more frequent heat events.
"What's more unique about this is the duration", said Kelly Hobelman, a meteorologist with Environment Canada. "We are looking at temperatures 30 or above all the way until Friday". Friday is forecast to be 28 C with a 40 per cent chance of showers.
To prevent heat stress during a heat alert, Dr. Strang suggests to stay in a shaded, cool or air-conditioned area, drink plenty of water, wear light-coloured clothing and to not leave anyone or any animal unattended in vehicles.
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Ryan Frashure said officers arrived within about 60 seconds and took the gunman into custody without an exchange of gunfire. Press Secretary Sarah Sanders added in a tweet: "Strongly condemn the evil act of senseless violence in Annapolis, MD ".