WASHINGTON, United States -- A relentless US heat wave that has triggered health alerts for more than 100 million people is set to intensify this weekend, with temperatures and humidity forecast to surge to suffocating highs in many parts of the country.

The devastating heat -- which has also hit Europe, causing hundreds of deaths there -- highlights the direct threat climate change poses to even the wealthiest countries on the planet.

"So far this week, 60 daily high temperature records have been tied/broken as dangerous heat enveloped much of the Nation," the National Weather Service (NWS) said in a tweet Thursday morning

"More records are likely to be set over the next week," it added.

Temperatures in large parts of the southwest United States have soared to over 100 degrees Fahrenheit (38 degrees Celsius), topping 110 degrees in some areas. Similar levels were recorded across the US south, where humidity compounded the discomfort.

The NWS tweeted Tuesday that 100 million people were under heat-related warnings and advisories, and said on Thursday that a "significant portion of the population" would remain under such warnings over the weekend.

Already high temperatures were set to rise further this weekend across the east coast of the United States, where high humidity could push "feels-like" temperatures well above 100 degrees.

Washington and Philadelphia have both declared heat emergencies, and warned their residents to remain vigilant.

"Stay hydrated, limit sun exposure, and check on seniors, neighbors & pets," Washington Mayor Muriel Bowser said on Twitter.

Philadelphia's Department of Public Health warned in a statement that "during hot weather, NEVER leave children and pets unattended in vehicles under any circumstances."

- More heat to come -

While the oppressive heat is expected to subside in the US south and east next week, a high pressure system over the Pacific northwest is expected to push temperatures 10-15 degrees above normal levels.

Temperatures have also soared in Europe, setting a new all-time record in Britain, where the national weather service clocked 104.5 degrees in eastern England, surpassing the previous high set in 2019.

Unlike much of western Europe, most homes in the United States have air conditioning, helping to mitigate the heat wave's health risks, but adding strain on the power grid in times of high usage.

In Texas, residents were asked last week to reduce their power consumption by not running major appliances from 2:00 pm to 8:00 pm, as the southern state's electric utility warned that low windspeeds threatened the grid reliability.

The City of New York on Thursday asked residents to use less energy by raising their air conditioning to 78 degrees and unplugging appliances.

Scientists have warned that heat waves like the ones being felt in the United States and Europe will become more frequent and rise in intensity due to global warming.

Though he campaigned on an agenda of robust action against climate change, US President Joe Biden's biggest plans have been stymied by the Supreme Court and lawmakers, including from his own Democratic party.

Biden announced in a speech Wednesday that his administration would redouble efforts to address global warming, but stopped short of declaring a formal climate emergency, which would grant him additional policy powers.