Chris Mitchell pours water over his head Tuesday to cool off while wearing a Darth Vader costume on the Las Vegas Strip. Mitchell was taking a break from posing for photographs with tourists.

PHOENIX — Don Kushner emerged from his afternoon hike on Camelback Mountain clearly a little run down from the heat.

Kushner was one of the few who ignored warnings to avoid strenuous outdoor activity and decided to exercise outside on one of the hottest days in Phoenix’s recorded history.

“Here it’s your own private mountain and it’s wonderful,” he said, covered in sweat Tuesday.

Phoenix authorities issued several warnings about the dangers of the heat. Phoenix park ranger Chris Webb said she saw about a dozen hikers on Camelback Mountain in the afternoon hours.

“I would recommend that people do something less strenuous than to come out to the toughest hike in Phoenix in the middle part of the day,” she said. “Maybe go swimming. Maybe do something indoors instead.”

The first day of summer brought some of the worst heat the southwestern U.S. region has seen in years.

Meteorologists said Tuesday’s temperature in Phoenix topped out at 119 degrees, a mark that’s only been matched or surpassed four other times in the city’s recorded history. The all-time high was 122 degrees on June 26, 1990.

Death Valley, Calif., reached 125 Tuesday and Palm Springs hit 121, still a degree lower than the same day last year.

The heat wave comes amid new research findings that nearly 1 in 3 people now experience 20 days a year when the heat reaches deadly levels.

The study of nearly 2,000 deadly heat waves worldwide since 1980 was published Monday in the journal Nature Climate Change.

Workers at a construction site in a Phoenix suburb huddled under the shade of an excavator during a break. At another building site, men in hard hats and yellow vests labored and sweated in the heat, downing water to stay hydrated.

Las Vegas also baked. Visitors tried to stay inside air-conditioned casinos. Others went to a bar where the temperature is set at 23 degrees and glasses, walls and seats are sculpted from ice.

Airlines have been taking measures to reduce the weight of jets. American Airlines spokesman Ross Feinstein said it is limiting sales to prevent the planes from exceeding maximum weight for safe takeoff in the hot conditions.