More than 150 million people are sweltering in sweltering heat on Friday in the eastern United States, including New York and Washington, with the heat wave threatening to impact the World Cup and the country's 250th anniversary celebrations.

As the United States observes a holiday ahead of its national holiday, authorities are warning of extreme temperatures expected in several major cities, where daily records were already broken the day before.

Combined with very humid air, the perceived heat should reach 45°C in New York and Washington and 40°C in Boston and Philadelphia.

"This level of heat can be deadly for those who do not have adequate air conditioning and who do not stay sufficiently hydrated," warned the New York State National Weather Service (NWS).

In Brooklyn, Daniel Jefferson, 39, wearing a cap, is busy despite the heat unloading boxes of food into the cellar of a restaurant.

"We haven't experienced anything like this in New York in a long time," this delivery man told AFP, complaining of "completely crazy" heat that was "tiring" him out.

- Party pooper -

This "dangerous and record-breaking heat wave" has been hitting the eastern half of the United States since the middle of the week and is expected to continue in several regions until Saturday, the 250th anniversary of the American Declaration of Independence, and cause severe thunderstorms on Friday and Saturday.

While many outdoor events are planned for this occasion, the weather could play spoilsport.

In Washington, the holding of a large concert in front of the Capitol seemed threatened and the opening of the festivities was delayed.

On Friday, the "grand fair" organized for the occasion on the huge esplanade of the Mall was temporarily closed after rescuers evacuated a young woman suffering from heatstroke.

Despite the sweltering heat, the national guards deployed by Donald Trump in the capital continue to patrol as best they can.

Taking refuge in the shade of a park, Lee Hernandez, a soldier originally from Puerto Rico, was trying to cool off.

Although accustomed to tropical temperatures, this heatwave seems "even worse" than the climate of his island, he told AFP. And the nearly "15 kilos" of equipment he's carrying, including a bulletproof vest and a weapon, only makes matters worse.

For Nazario, 52, who is in charge of maintaining Washington's green spaces, the heat wave hasn't changed anything about his work. "I try to drink a little water all the time so I don't get dehydrated," he told AFP, wearing a hat and a water-soaked towel around his neck.

- Stadiums without air conditioning -

This stifling heat could also affect the football World Cup currently taking place in the United States, as well as in Canada and Mexico.

While some World Cup stadiums are equipped with a roof and air conditioning (Atlanta, Dallas or Los Angeles), many are open-air, like the one in Philadelphia, where France will face Paraguay on Saturday in the round of 16.

The teams from Argentina and Cape Verde could also suffer the consequences in Miami on Friday, as the stadium lacks air conditioning. At 6:00 PM local time on Friday, the scheduled kickoff time, the perceived temperature is expected to be 38°C (100°F), according to forecasts.

Although a majority of buildings in the United States are equipped with air conditioning and cooling systems, heat waves cause more deaths in the country than hurricanes and floods.

And this heatwave episode is of particular concern to the authorities because of its length and intensity which could affect the health of vulnerable people and damage infrastructure such as electrical networks.

Around the world, heat waves are becoming more intense and more frequent due to climate change, primarily caused by the burning of coal, oil and gas.

On Friday, US weather authorities warned of the possibility of an extreme heat wave hitting the western half of the United States starting in mid-July.