A punishing heatwave has settled over central and eastern parts of the US and Canada, pushing temperatures as high as 37C (99F) and causing up to 22 deaths.
The US weather service warned of "dangerous" levels of heat and humidity creeping east on Friday, with no relief 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.
Many regions in the central US and parts of the eastern seaboard have seen heat indexes - a combination of temperature and humidity - topping 43C.