Heat-wave spreads across central and eastern US

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 warning, 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.

"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, was reported as saying by 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.

Meanwhile, asphalt and concrete pavements and buildings in cities were "re-radiating" the heat, he added. "There's no good place to be.”

Heat is the number one weather-related killer in the US, according to the National Weather Service.

Across the central and eastern US, people and animals alike have been struggling to keep cool amid the oppressive heat and humidity.

As the heat peaks in major population centres on the east coast, the number of deaths is expected to rise, officials warn.

Jacks said the combination of high heat and high humidity made it hard for the human body to cool itself - because sweat does not evaporate efficiently.

In the town of Hutchinson in Kansas three elderly people were found dead in separate homes on Wednesday, while the body of a woman in her 80s was found in her bedroom in the nearby state of Missouri.

In Minnesota - a northern state known for its frigid winters - farm livestock have been dying from heat stress at a rate not seen in three decades, the Minneapolis Star Tribune newspaper reported. Turkeys were hit especially hard, the paper reported.

In South Dakota, as many as 1,500 head of cattle have died in the heat, state veterinarian Dustin Oedekoven told Reuters news agency.