More than 170m Americans under heat alerts as heatwave expands

Between 250 and 275 million will face heat indexes of 90F as heatwave moves into parts of Great Plains, midwest and north-east

• US heatwave: follow live

Over 170 million Americans are under heat alerts this week, according to the National Weather Service, as a heat wave that has affected the southern US for weeks has expanded into parts of the Great Plains, midwest and north-east US.

Between 250 and 275 million people in the US will face heat indexes of at least 90F (32C), as the US braces for the hottest weather of the summer averaged across the country.