Tens of millions of Americans sweltered under furnace-like temperatures Tuesday as central and eastern cities hunkered down for a heat wave set to last through the July 4 holiday weekend.

Dozens of local temperature records could be broken, the National Weather Service (NWS) warned, with temperatures in many places to surpass 38 degrees Celsius and high humidity pushing the heat index as high as 115 degrees.

It comes as America prepares to celebrate its 250th anniversary of independence, and as the United States along with Canada and Mexico co-host the World Cup soccer tournament amid the extreme heat.

Chicago, the nation’s third-largest city, announced it was opening cooling centers and sending city employees to carry out wellness checks on vulnerable populations.

In New York, Mayor Zohran Mamdani’s office said it was launching an “unprecedented, historic” plan to deal with the heat that includes vans to provide residents with hydration, as well as “pop-up” cooling stations with misting fans and cooling towels.

Washington, the capital, meanwhile was forecast to see 38C temperatures from Thursday through Saturday, when it will host a fireworks display on the National Mall that organizers said would be the biggest in history.

More than 60 million people are currently under heat alerts, the NWS said.

Health agencies are urging citizens to watch for signs of heat-related illness, ranging from cramps and exhaustion to life-threatening heat stroke.

Child hot-car deaths are another concern, with nine such deaths reported so far this year in the United States, against an average of 37 annually, according to the National Safety Council.

Pets are also at risk, with authorities recommending dogs remain indoors except for bathroom breaks, and warning owners to watch for hot asphalt that can burn paws.

In World Cup news, numerous knockout-stage matches will be played under oppressive heat, including France v Sweden at New York New Jersey Stadium and Norway v Cote d’Ivoire in Dallas on Tuesday.

The weather has already had an impact: France was forced to sit through a two-hour storm delay during its group-phase match against Iraq.

Two group-stage matches were played in temperatures exceeding the threshold at which the global players’ union recommends games be postponed or delayed, while dozens of fans have been treated for heat illness in Houston and Miami.