The United States is sweating through a weekend of extremely hot weather, with major cities including New York and Washington bracing for temperatures close to or exceeding 100 degrees Fahrenheit (38 degrees Celsius).
Nearly 150 million people across the country are facing hazardous temperatures in a heatwave stretching from the Midwestern plains to the Atlantic coast, the National Weather Service (NWS) said.
Heat index values could reach 110 to 115 degrees, particularly in the east, the weather service said Saturday.
It warned that "dangerously high temperatures and humidity could quickly cause heat stress or heat stroke if precautions are not taken."
People were urged to stay hydrated, watch out for the sick and the elderly, stay inside as much as possible and not leave children or animals in cars.
The heatwave has already claimed six lives, including four in the eastern state of Maryland, CBS affiliate WJZ reported.
Heat warnings have also been issued for parts of eastern Canada.
New York City has opened 500 cooling centers for residents to escape the extreme weather.
"Saturday is going to be really, really bad, on through Sunday," said Mayor Bill de Blasio in a warning to the city.
"Don't go out in the heat if you don't need to," he said. "This is serious, serious stuff."
Organizers cancelled the New York City Triathlon for the first time since the event's founding in 2001, citing "severe heat warnings, continued heavy rainfall and thunderstorm watches."
In Washington, the morning low of 81 degrees was just one degree below the record set in 2015, with "a good chance to hit 100 today for the first time since 2016," The Washington Post reported.
Temperatures soared earlier in July in the northwestern state of Alaska, which straddles the Arctic Circle, with largest city Anchorage hitting an all-time high of 90 degrees.
Alaska is warming at twice the rate of the global average, scientists say.
Climate data showed June was the hottest month on record worldwide, with a heatwave across Europe smashing national records.