The Nevada Division of Emergency Management warned residents not to rely on fans to stay cool and urged them instead to seek air-conditioned spaces such as libraries, shopping malls or the cooling centers that have been opened across the Southwest in recent weeks.

New York Gov. Kathy Hochul activated 50 members of the National Guard to help boost the state’s response. New York City’s more than 500 cooling centers are set to open Tuesday.

“We are going to be seeing temperatures at levels we have not seen in our lifetimes,” Hochul said in a statement Monday, adding: “This could be a deadly event. Extreme heat is the leading cause of weather-related deaths.”

The NWS’ Phoenix branch said temperatures reached 112 degrees there Sunday — 7 degrees above average and just under the record of 115.

“The duration of this heat wave is notable and potentially the longest experienced in decades for some locations,” the Weather Prediction Center said Sunday.