• See more Daily Mail on Google - save us as a Preferred Source

A record-setting heat dome is blanketing half the US, exposing roughly 70 million people to triple-digit temperatures that could rapidly become deadly.

The massive high-pressure system has settled over at least 15 states, including parts of California, Arizona, Nevada, Utah, Colorado, Oregon, Idaho, Montana, Wyoming, New Mexico, Texas, Minnesota, Nebraska and the Dakotas.

Widespread extreme heat warnings have been issued in multiple states, including California, Arizona, Nevada, Utah and Colorado, and are expected to remain in effect through at least Sunday, with some areas seeing record heat lasting until late next week.

Las Vegas and Phoenix are expected to see temperatures surpass 115 degrees Fahrenheit throughout the weekend, and parts of Southern California could hit 120.

The National Weather Service (NWS) has warned that the risk of dehydration and heat stroke will be so severe in these areas that the safest thing to do is avoid drinking alcohol, eating meals high in protein or sitting in cars for any length of time.

'Car interiors will reach lethal temperatures in a matter of minutes,' the agency warned in a statement Friday.

Extreme heat soaring past 120F can cause the human body to struggle to cool itself through sweating alone, which sends your body temperature rising and causes heat stroke - a life-threatening emergency where the body’s systems start to fail.

This can happen even faster inside a car, which becomes a mini greenhouse, with temperatures reaching over 150F in a matter of minutes. Hot cars are especially deadly for young children and pets.

A massive heat dome over 15 US states has triggered extreme temperature warnings, increasing the risk of heat stroke and other illnesses (Stock Image)

Approximately 70 million people are trapped under the high pressure system causing temperatures to rise to more than 115 degrees Fahrenheit

The heat dome traps warm, humid air, keeping it from rising to allow the US to cool down, sending temperatures throughout the region soaring between 10 and 20 degrees above their normal averages for late July and early August.

AccuWeather has predicted that Las Vegas will see its daily temperature record shattered for five straight days, starting Saturday when the high is expected to reach 117F.

Phoenix is expected to break its record for heat on Friday, Saturday and Sunday, surpassing 115F each day.

The NWS warned: 'Heat-related illnesses increase significantly during extreme heat events. Take extra precautions when outside. Wear lightweight and loose-fitting clothing.'

'Try to limit strenuous activities to early morning or evening. Take action when you see symptoms of heat exhaustion and heat stroke,' officials added.

Heat exhaustion, when the body overheats from prolonged exposure to heat, often starts with heavy sweating, fatigue, developing cool, pale, clammy skin and a fast, weak pulse, muscle cramps, dizziness, nausea and headaches.

As for heat stroke, which is far more deadly and can develop within 15 minutes in extremely hot conditions, the first symptoms are often a throbbing headache, confusion, slurred speech, nausea, dizziness, and a fever above 103 degrees Fahrenheit.

Sufferers may also develop red, dry, or damp skin, a rapid pulse, and lose consciousness. It turns fatal when the body's organs begin to fail.

Pictured: Tourists battle to stay cool while visiting the Las Vegas welcome sign amid the recording-setting heat wave

The heat is expected to be so bad, officials recommend avoiding alcohol and high-protein meals

Move anyone affected by these conditions into a cool, shaded spot right away and call 911.

The NWS noted that elderly adults, children and those with chronic health issues and mental health conditions face the greatest risk. They are urged to stay indoors and use air conditioning.

Other major cities expected to feel the heat this weekend include Los Angeles, which could reach 100F, San Diego, Salt Lake City, Tucson and Palm Springs.

For areas where the temperature reaches 115F and hotter, AccuWeather warned that most outdoor activity should be considered dangerous.

Along with heat exhaustion and heat stroke, the average person is also more likely to suffer cramps and dehydration quickly without taking frequent rests in shade and drinking water.

The heat dome is also expected to combine with strengthening winds in the Northwest, sending the risk of wildfires in several states skyrocketing.

The extreme heat wave is expected to cause wildfire risks in several states surge this weekend

Pictured: Wildfires in Oregon burning on July 25. Over one million acres is reportedly on fire throughout the Pacific Northwest

AccuWeather's expert meteorologist Chad Merrill added that the fire danger will also spread east, as the extremely dry conditions set off more fires and winds push the smoke towards the Northern Plains, Midwest, Great Lakes and Northeast throughout August.

Merrill said in a statement: 'Uncontrolled wildfires that are burning in an area where the jet stream winds are persistently strong will blow smoke downwind of the source region, usually to the east.'

'The smoke can be thick enough to obscure the sun during the day and lead to cooler high temperatures. In this case, the air quality suffers.'