Millions of Americans are sweltering as experts warn early heat could herald next record-smashing summer

With the official start of summer still weeks away, a potentially record-setting heatwave is cooking the south-western US, causing dangerous conditions far earlier than normal.

Excessive-heat warnings have been issued from the southern tip of Texas across Arizona and Nevada, and up through the center of California to the northern part of the state, as more than 36 million people across the country brace for days of potentially life-threatening temperatures. Affected areas of California could see conditions of 30F higher than normal for this time of year, as south-west cities, including Phoenix and Las Vegas, prepare to hit peaks above 110F.

Experts have warned this could be just the start of another record-smashing season with the potential to usurp 2023 as the world’s hottest year. A three-month outlook on seasonal temperatures published by the National Oceanic and Atmospheric Administration (Noaa) in mid-May forecasts above-average temperatures for most of the country through the summer.