The first heat wave of the year is expected to maintain its grip on the U.S. southwest for at least another day Friday, after records tumbled across the region with temperatures soaring past 43 C from California to Arizona.

Although the official start of summer is still two weeks away, roughly half of Arizona and Nevada were under an excessive heat alert, which the National Weather Service extended until Friday evening. The alert was extended through Saturday in Las Vegas, where it’s never been hotter this early in the year.

“High temperatures as much as 10 to 15 degrees [Fahrenheit] above normal can be expected, with record high temperatures likely for some sites through Friday,” the weather service in Las Vegas said. Temperatures will slowly retreat over the weekend, but will remain above normal into early next week.

“It’s so hot,” said Eleanor Wallace, 9, who was visiting Phoenix from northern Utah on Thursday on a hike celebrating her birthday with her mother, Megan Wallace.

The National Weather Service in Phoenix, where the new record high of 45 C on Thursday leapfrogged the old mark of 44 C set in 2016, called the conditions “dangerously hot.”

Heat affects 11 at Trump rally

There were no immediate reports of any heat-related deaths or serious injuries.

But at a campaign rally for presumptive Republican presidential nominee Donald Trump in Phoenix, 11 people fell ill from heat exhaustion by late afternoon and were taken to the hospital, where they were treated and released, fire officials said.

Las Vegas set a new record of 43.8 C on Thursday that also equalled the earliest time of year the high reached at least 43.3 C. The Clark County Fire Department said it had responded to at least 12 calls for heat exposure since midnight Wednesday. Nine of those calls resulted in a patient needing hospital treatment.

Several other areas of Arizona, California and Nevada also broke records by a degree or two, including Death Valley National Park with a record high for the date of 50 C topping the 49.4 C dating to 1996 in the desert, which sits 59 metres below sea level near the California-Nevada line. Records there date to 1911.

The heat has arrived weeks earlier than usual even in places farther to the north at higher elevations — areas typically a dozen degrees cooler. That includes Reno, where the normal high of 27 C for this time of year soared to a record 37 C on Thursday. Records there date to 1888.

The National Weather Service forecast mild cooling region-wide this weekend, but only by a few degrees. In central and southern Arizona, that will still mean temperatures getting as high as 43 C.

Trying to beat the heat

On Thursday in Phoenix, the unseasonably hot weather did not prevent Oscar Tomasio of Cleveland from proposing to his girlfriend, Megan McCracken, as they sweltered to the peak of a trail on Camelback Mountain with three litres of water each in tow.

“It was a grueling hike,” Tomasio told The Associated Press. “It was extra hot, so we started extra early.”

“The views were beautiful. We didn’t make it quite to the top because she was a little nervous with the heat,” he said. “So I proposed to her when the sun rose.”

McCracken confirmed they’d planned a sunrise hike and awoke about 5 a.m. local time in an effort to beat the heat and an impending closure of the trail.

“Probably not early enough,” she said.

Megan Wallace, mother of the birthday girl from Utah who also came packing water bottles, said: “We started just a few minutes after six and it’s like we came prepared, but we got through all of our water and it was hot — was hotter than we’re used to.”