113 million Americans are currently under heat advisories as parts of the US are expected to see record temperatures on Sunday.
The advisories have been issued across the country from as Florida on the East Coast to California in the West and as far North as Washington state.
Authorities have also warned of “dangerous” heat levels into next week across the south-west.
The country’s National Weather Service (NWS) has urged people not to underestimate the risk to life.
Phoenix, Arizona rcorded a sweltering high 48C on Saturday.
It means temperatures have hit at least 43C for 16 days straight, with mobile clinics reportedly treating homeless people suffering from third-degree burns.
Meanwhile, Death Valley in California – one of the hottest places in the world – is forecast to reach 54C, nearing the hottest temperatures ever reliably recorded on Earth.