A punishing heat wave has settled over central and eastern parts of the US, pushing temperatures as high as 43C (110F) and causing up to 22 deaths.

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.

"This is an exceptionally strong ridge of high pressure that really has an exceptional scope and duration," Eli Jacks, a meteorologist with the National Weather Service, told the BBC.

"The air is sinking, as it sinks it compresses and gets warmer." It also dries out, so few clouds form to block the high early-summer sun, he said.

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