Around 1.2 million people were under extreme heat risk on Saturday, meaning temperatures are expected to stay dangerously high with no relief overnight.
The largest area under the warning is around Tucson, Arizona, where the National Weather Service forecast dangerous highs between 39 and 42 degrees Celsius. Areas of inland Southern California also faced extreme risk.
Another 18.6 million are under major heat risk, affecting workers and anyone without regular cooling and hydration, including in Miami.
Portland, Oregon, reported a record high on Friday, according to preliminary data. Struggling through the smothering heat were long-distance runners who were passing a baton in a relay race from inland Mt Hood to the Pacific Coast.
At least one long-distance runner competing as part of a group of athletes over 50 years old in Portland's annual "Hood to Coast" event lost consciousness and was hospitalised on Friday after running 6.4km.
The preliminary report of 102 degrees in Portland, if upheld, would break the 36.7C high for Friday, set in 1942, according to the NWS.Â
The inland Oregon city recorded a high of 46C in June 2021. More than 100 people died in the surrounding area during that heatwave. The majority of the victims lived alone, and the vast majority were 60 or older, but the youngest was 37.
