Much of eastern Canada remains under blanket of hot, humid air

Extreme heat warnings have been issued across southwestern Ontario

The extreme heat was expected to ease off on Friday with the passage of a cold front.

They planned to visit thousands more as the heat was expected to continue until Friday.

Heat warnings are issued by Environment and Climate Change Canada to inform the public when air temperature and humidex are forecast to be above a certain criteria for two consecutive days. "Humidex values will be in the mid to high thirties today, and near low forties for Wednesday and Thursday".

While coastal areas can expect cooler conditions, overnight lows will struggle to fall between 18 or 19 C degrees.

The extreme heat event will continue through Thursday.

Tuesday night is expected to have a low of 22 with some 20km/h winds in the evening.

The heat wave has hit the Atlantic provinces, too - a heat warning is in effect for Halifax as Nova Scotia has been experiencing temperatures of around 30 degrees, or up to 39 degrees with the humidex.

And if the heat wasn't enough, the forecast also calls for a 60 per cent chance of rain this afternoon while humidity levels stay high. Low temperatures overnight will again be in the high teens to low 20s providing little relief from the heat.

This will be the most significant heat event in the past few years. The risks are greater for young children, pregnant women, older adults, people with chronic illnesses and people working or exercising outdoors.

The record-high temperature pattern is expected to continued through Thursday, with heat indexes - the "feels like" temperature when accounting for humidity - reaching up to 110 degrees in some parts.

There are many warning signs for heat illness, including swelling, rash, cramps, fainting, heat exhaustion, heat stroke and the worsening of some health conditions.