LOS ANGELES (AFP) - A scorching heatwave in the western United States has grounded flights, caused fires and prompted power outages, with record temperatures expected on Tuesday (June 20) in several states including Arizona and Nevada.

The extreme temperatures prompted American Airlines on Tuesday to ground 43 flights to and from Phoenix Sky Harbor Airport, where temperatures were expected to reach 49 deg C.

Company spokesman Ross Feinstein told AFP the flights were run by two regional partners - Skywest and Mesa - which operate smaller airplanes that cannot take off when temperatures reach a certain level.

"Each aircraft has different International Standard Atmosphere (ISA) performance specifications, which is set by the aircraft manufacturer," Feinstein said.

"This also takes into account the elevation at the airport.

"For Phoenix, that is limited to 118 degrees."

He said the airline's other mainline flights, which concern larger jets, had not been affected by the blazing temperatures.

The soaring heat has affected much of the western United States where triple-digit temperatures were expected throughout the week, a spokeswoman for the National Weather Service said.

"We are expecting temperatures in the neighbourhood of 120 degrees F (49 deg C) in Nevada and in southern California today," Bianca Hernandez told AFP.

"Temperatures will pretty much stay in the 110-115 range for the next coming week," she added.

The heat has led to electricity outages in several parts of California, as more people turn on air conditioners to battle the heat, overtaxing the power system.

Several wildfires were also burning in the state.

"If you can avoid being outside in general, that's the best thing you could do today," Fernandez said.

"Everyone should hydrate, and if you have to be outside, try to do so before the sun rises or after sunset."