This picture taken on July 26, 2015 shows a child playing in a fountain on a square to cool himself amid a heatwave in Binzhou, eastern China's Shandong province.   CHINA OUT     AFP PHOTO        (Photo credit should read STR/AFP/Getty Images)
What NOT to do in a heat wave
01:14 - Source: CNN
CNN  — 

A dangerous heat wave is expected to grip California and parts of the southwest Friday and into the weekend, threatening millions of people and likely fueling existing wildfires.

More than 25 million people are under excessive heat watches, warnings or advisories, including in Los Angeles, San Diego, Las Vegas, and Phoenix metro areas.

The scorching heat will bring triple-digit temperatures to Los Angeles, where the mercury is forecast to reach 105 degrees on Friday and 100 on Saturday, CNN meteorologist Haley Brink said.

Over a dozen record highs are forecast to be broken Friday afternoon across California. Areas directly along the coast seeing temperatures in the 90s and inland areas hitting the triple digits, Brink added.

The National Weather Service is urging residents to reduce time in the sun, drink plenty of water and especially don’t leave children or pets in cars.

Fire threat

More than 4,000 firefighters are battling several wildfires in California and the extreme heat is likely to complicate things for them.

For example, the County Fire in California, which has charred 88,000 acres in Yolo and Napa counties and is only 30% contained, is one of several blazes with potential to grow as the weather gets hotter and drier into the weekend, Cal Fire said.

And strong winds could make conditions even worse.

“The extreme heat in combination with single-digit humidities and gusty north winds will likely bring critical fire weather conditions across the mountains, Santa Barbara south coast, Santa Clarita Valley, San Fernando Valley, and Santa Monica mountains,” the weather service said.

Forecasters expect winds of 35 to 45 mph with isolated gusts up to 50 mph.

Heat takes dozens of lives

A woman tries to shield herself from the sun in Philadelphia, Pennsylvania.

A heat wave that swept across parts of Canada this week killed 54 people in the province of Quebec, according to health officials. Twenty-eight deaths occurred in Montreal, said Marie-Claude Lacasse with the Ministry of Health.

Many victims in Montreal were mostly over the age of 50, male, were living alone and had no air conditioning, said Dr. David Kaiser of Montreal’s Regional Public Health Department.

CNN meteorologist Taylor Ward said the region had seen record high temperatures and high humidity since Sunday. Temperatures were in the mid-90s for Montreal on Sunday and Monday, about 20 degrees higher than the normal temperatures this time of year.

Montreal health officials opened 19 cooling stations in public health and social services buildings across the city, and asked people to call public transport services to get a ride to one of the air-conditioned centers.

Several heat-related deaths were also reported in the US since last weekend. In Pennsylvania, a woman died of heat-related causes on Saturday in Pennsylvania while working in her garden, according to the Blair County coroner’s office. The woman went into cardiac arrest at her home and died at a hospital.

A 30-year-old man died after he collapsed on a mountain trail while running a race in Wilmington, New York, the Essex County coroner said. At the emergency room the man’s internal temperature reached 108 degrees, damaging his brain.

“When your brain becomes overheated like that, it can’t function any more,” Essex County Coroner Frank Whitelaw said.

In addition, two possible heat-related deaths were being investigated in Kansas City, Missouri. The deaths involve a man in his 80s, who died Monday, and a woman in her 40s, who died last week, according to the Kansas City Health Department.

CNN’s Joe Sutton and Eric Levenson contributed to this report.