Los Angeles, California - Some 44 million Americans were under a heat wave warning on Saturday as parts of the US are expected to hit 110 over the weekend.
The temperatures, well above seasonal averages, could break records, the National Weather Service (NWS) warned.
"Dangerous heat is expected to unfold through the weekend with triple-digit highs and potential for daily maximum temperature records both days," the service's Weather Prediction Center said Saturday.
On Sunday, temperatures are expected to reach between 100 and 110 in several northern states, including Montana and North Dakota.
The blistering heat also has hindered efforts to fight massive wildfires raging in Colorado and Utah.
The weather was also broiling the southeastern US, including Miami, which was hosting Saturday's England-Norway World Cup quarterfinal match.
Just a week ago, the East Coast was gripped by another heat wave that pushed temperatures to around 104 in New York and Philadelphia.
Around the world, heat waves are becoming more common and intense due to climate change, primarily caused by the burning of coal, oil, and gas, and the emission of greenhouse gases.
Western Europe experienced its hottest June on record. The heat wave left more than 1,300 people dead across the region, according to the World Health Organization.
In France this weekend, the Eiffel Tower and other Paris landmarks announced early closures as a quarter of the country was sweltering under the third heat wave to hit the country since May.