Four people are dead in Arizona amid a dangerous, ongoing heat wave that's extending to several Southwest states.

Two hikers died Sunday in Pima County, Arizona, due to heat-related illnesses, the Pima County Sheriff's Office said. A 28-year-old trainer died from heat exhaustion Sunday after she mountain biked at the Phoenix Mountain Preserve, according to the Phoenix Fire Department said. A man died of heat exposure after hiking the Superstition Mountains Saturday, the Pinal County Sheriff said.

Temperature records were shattered Sunday in dozens of cities in New Mexico, Arizona, Nevada and California.

Yuma, Arizona, hit 120 degrees; Phoenix, Arizona hit 118 degrees; Palm Springs, California, reached 118 degrees; and Burbank, California, reached 109 degrees.

Previous records were hit in Albuquerque, New Mexico (103 degrees) and North Las Vegas, Nevada, (109 degrees).

Monday is expected to be the hottest day of the week as temperatures in some areas will rise above 120 degrees. Utah, Nevada, California and Arizona are facing excessive heat warnings and advisories.

The extreme heat is also hindering firefighters who are trying to contain large fires in New Mexico, Arizona and California.

The record heat also impacted plane travel. A United Airlines flight operated by Mesa Airlinesdeparted Houston's George Bush Intercontinental Airport Sunday afternoon and was minutes away from landing at Sky Harbor Airport in Phoenix when the flight crew notified passengers it would be turning back due to the weather.