A heat-wave has settled over central and eastern parts of the United States, pushing temperatures as high as 43C 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.
Officials said as much as 50% of the population was under a heat advisory notice.
Meteorologists attribute the temperatures to a ''dome'' of high pressure in the atmosphere.
National Weather Service meteorologist Eli Jacks told the BBC that heat was ''the number one weather-related killer'' in the US.
Mr Jacks says the combination of high heat and high humidity makes it hard for the human body to cool itself because sweat does not evaporate efficiently.
In Minnesota, the Minneapolis Star Tribune newspaper reported that farm livestock have been dying from heat stress at a rate not seen in three decades. Turkeys were hit especially hard.
The BBC reports that high temperatures are responsible for killing 162 people in the United States on average each year.
A heat-wave during the Great Depression in 1936 was blamed for more than 5,000 deaths in the US and Canada.
