A punishing heat-wave has settled over central and eastern parts of the US, pushing temperatures as high as 37C (99F) and causing up to 22 deaths, BBC reported.
The National Weather Service warned of "dangerous" levels of heat and humidity creeping east, with no relief expected in eastern states until Sunday.
As much as 50% of the US population was under a heat advisory, officials said.
Meteorologists have put the temperatures down to a "dome" of high pressure in the atmosphere.
On Thursday, many regions in the central US and parts of the eastern seaboard also saw heat indexes - a combination of temperature and humidity - topping 43C.