The first major heatwave of the summer is intensifying across the eastern half of North America, triggering health alerts and disrupting daily life for millions.

Heat warnings are in effect from the US Midwest to the East Coast, as well as in parts of Ontario, Quebec and Nova Scotia in Canada, impacting more than 160 million people through the week.

Experts warn that the soaring temperatures could aggravate the risk of heat-related illness, especially due to high humidity levels.

Compounding the danger is the extended duration of the event, with little nighttime relief - temperatures in some eastern cities may remain above 80F (27C) overnight.

The heatwave arrives less than a week after the official start of summer. Forecasters say several places may experience record highs.

The Mid-Atlantic region is expected to face the most intense conditions by Thursday, followed by the eastern Ohio Valley into Friday. Several consecutive days of oppressive heat in these areas could significantly increase health risks.

The US National Weather Service (NWS) has warned people to "take action when you see symptoms of heat exhaustion and heat stroke".

People are advised to stay out of the sun during the hottest times of day, drink plenty of water, and to check on vulnerable individuals, including the elderly and those with pre-existing health conditions.

Although spells of extreme heat affect many parts of North America each summer, this heatwave could surpass June records in places.

In New York, highs on Tuesday may reach 101F (38C) which would equal the highest June temperature ever recorded in the city, dating back to 1966.

Energy companies on the east coast have appealed to customers to conserve power, due to fears of blackouts, as millions crank up their air conditioning units to high. (BBC)

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