Approximately 162 million people -- nearly one-half of the US population -- were living in areas under active heat warnings, according to the National Weather Service.
It said in a post on X the "dangerous heat" was expected to remain in the western part of the country for the rest of the week before moving eastward over the weekend, warning "the persistent and record-breaking heat is extremely dangerous to those without access to cooling."
Among places that saw records shattered was Las Vegas, Nevada, which recorded its all-time high temperature of 120 degrees Fahrenheit (48.9 degrees Celsius) on Sunday.
In Texas, the White House declared a federal emergency after the storm Beryl had left some 2 million without power as of Tuesday evening.
"The greatest concern right now is the power outages and extreme heat that is impacting Texans," President Joe Biden said in a statement.
Meanwhile the southeastern United States and East Coast saw sweltering temperatures of their own, with heat advisories and excessive heat warnings in effect from Florida to Massachusetts.
The heat has been directly attributed to several deaths along the US West Coast.
In Death Valley, California, on Saturday, a motorcyclist died of suspected heat exposure and another was hospitalized, according to National Park Service officials.
The area, known as one of the hottest places on Earth, recorded a temperature of 128F (53C).
Further north, four men in the Portland, Oregon area have died since Friday as a result of heat-related illnesses, according to local newspaper The Oregonian.
Records smashed
Though the Pacific Northwest is known as being generally more temperate than the deserts in the US Southwest, temperatures there remained elevated Tuesday after the Oregon capital Salem hit a daily record of 103 degrees (39.3 degrees Celsius) over the weekend.
"This is a record-breaking heat wave," Daniel Swain, a climate scientist with the University of California, Los Angeles, said during an online news conference over the weekend.
Some people in California, he said, had seen "not only the hottest day they've ever experienced but also the hottest day that their parents or grandparents ever would have experienced."
The high temperatures also contributed to extreme fire conditions in California, where thousands of acres burned in active wildfires up and down the state.
Northwest of Santa Barbara, the Lake Fire burned nearly 27,000 acres (110 square kilometers), prompting evacuations and road closures Tuesday.
The heat wave comes in the aftermath of the Earth's hottest June ever recorded, according to the EU's Copernicus Climate Change Service.
Recurring heat waves are a marker of climate change caused by humanity's use of fossil fuels, according to scientists.
