Julie Jacobson / AP Four-year-old Hayden Slykhuis cools off in the flow of a fountain at the Red Ridge Park kids water park in Las Vegas on Saturday.

More record-breaking temperatures were forecast for western parts of the United States Sunday, part of extreme weather that has already caused at least one suspected heat-related death.

Temperatures will continue to soar well into the 110s and even 120s into the new week ahead across the Southwest, Weather.com forecasters warned Sunday, raising fears that more people could fall victim to the excessive heat.

Hot temperatures will also spread throughout the valleys of the Great Basin and Northwest, but not to the levels witnesses in the Desert Southwest, it said.

Saturday saw a slew of weather records broken, Weather.com reported, including in Phoenix, Ariz. which saw its fourth-hottest day in history with a temperature of 119 degrees.

Salt Lake City, Utah, had its hottest ever day on record – 112 degrees for the second day in a row, while San Antonio, Texas set a new June record (108 degrees), as did Bush Intercontinental Airport in Houston, Texas (107 degrees).

Las Vegas' McCarran airport tied a record for the day at 115 degrees, and at a National Weather Service office in the southwest section of the city the thermometer spiked up to 118 degrees. In Death Valley, Calif., it was 124 degrees.

A Las Vegas Fire & Rescue crew responded to a report of an elderly man in cardiac arrest at residence without air conditioning on Saturday. When paramedics arrived, they found the man was dead, NBC station KSNV reported. The man, who was not identified, did have medical issues but paramedics characterized his death as heat-related.

Another elderly man whose car air conditioner went out while on a road trip fell sick, stopped and called 911. He was admitted to the hospital and reported in serious condition.

It was so hot in Nevada that rangers at Lake Mead persuaded tourists not to hike, according to the National Park Service, which posted the warning on its Facebook page.

Some cities have seen temperatures soar far past the hundred degree mark, while the heat continues. TODAY's Dylan Dreyer reports.

Dr. Kein Reilly with University of Arizona Department of Emergency Medicine told NBC News Tucson affiliate KVOA that Arizona residents should stay inside and drink plenty of water.

"If you get dizzy or light headed those are some signs of dehydration. If you become confused that's a real warning sign. That's someone who needs to come into the emergency department," Reilly said.

Cooling stations were set up to shelter the homeless as well as elderly people who can't afford to run their air conditioners, Phoenix, Ariz, Sheriff Joe Arpaio told NBC News affiliate KSNV.

NBC News’ Jeff Black contributed to this report.

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