Record-setting heat is suspected in 25 deaths from the Deep South to the Midwest to the East Coast, authorities said, with the temperature highs also suppressing some Fourth of July celebrations.

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Nearly 156 million people in the eastern two-thirds of the nation were under heat alerts issued by the National Weather Service on Saturday. A high-pressure dome of heat parked over the country was pushing air downward, heating it as it descends and resulting in temperatures of more than 100 degrees in some places, including the District of Columbia; Norfolk, Virginia; and Raleigh, North Carolina.

In Washington, D.C., which was hosting Salute to America 250 festivities at the National Mall celebrating a Fourth of July that marks 250 years of independence, emergency workers and members of the National Guard were seen rendering aid to attendees with heat-related ailments.

A man yelled, “Emergency! Coming through!” as he helped clear the crowds for a woman on a stretcher.

General seating was under a beating sun, and the temperature of chairs was measured at 160 degrees. Pallets of bottled water were seen stocked in the sunlight.

A joint information center spokesperson at the National Mall said the number of heat-related patients there would be released later.

Festivities were also delayed after the Homeland Security and Emergency Management Agency urged attendees to seek shelter immediately due to a severe thunderstorm that was moving overhead. Festivalgoers rushed to white tents for shelter.

The thunderstorms are part of a clash of warm and cooler air that is producing the unsettled cells from parts of Missouri to Pennsylvania.

More than 72 million were under severe thunderstorm watches on Saturday, according to federal forecasters, with the unsettled cells capable of producing winds 65 mph and greater, as well as quarter-sized hail. Damaging wind gusts were reported across Nebraska and Iowa.

A diagonal collection of states from Arkansas to Michigan to New York was the location of power outages for more than 900,000 utility customers on Saturday, according to utility tracker PowerOutage.us.

Michigan led the numbers, with more than 305,000 in the dark. New Jersey was next, with more than 124,000, followed by Missouri, with more than 100,000, according to the tracker.

The National Weather Service said cool air from the north will push the heat dome, responsible for a heat wave that started midweek, south and west in the coming days, relieving some of the most extreme temperatures in the Northeast.

But, it warned in a forecast discussion, “dangerous overnight warmth and high humidity continue to exacerbate heat-related impacts.”

New Jersey’s heat-related death toll rose from 19 to 22 on Saturday, state health department spokesperson Dalya Ewais said. The fatalities, mostly of people in their 30s to 80s, took place in 10 counties, predominantly in the central and northern portions of the state, she said.

“This is not a typical summer heat wave,” Ewais said in a statement. “This type of heat can quickly become life-threatening to humans and to animals of all ages.”

Earlier Saturday, health commissioner Dr. Raynard Washington described the conditions some of the dead were found in.

“Unfortunately, many of these individuals were found in homes without air conditioning,” he said at a news conference held by Gov. Mikie Sherrill. “Few were outside of their residence, some on the street and some even in parked cars.”

Resources, including chillers and generators, were being sent to health care facilities “in distress,” Washington said.

“In some cases, where we have to, we are working to evacuate patients from facilities where necessary,” he said.

One heat-related death was reported in Cook County, Illinois, government spokesperson Natalia Derevyanny said. The cause was reported as organic cardiovascular disease with heat stress as a contributing factor, she said.

Hinds County, Mississippi, reported the death of Mitchell Ray Cooley, 74, due to heat exposure on Thursday, state officials said. Cooley was the subject of a Silver Alert bulletin released by the Mississippi Bureau of Investigation after he was reported missing. His body was found the next day behind a gas station, the county coroner said in a statement.

“Mr. Cooley suffered from a medical condition that impaired his judgment,” the coroner’s office said.

On June 27, Martha Irene Van Egmond, 83, died in Bolton, a small town about 200 miles north of New Orleans. Hinds County’s chief death investigator, Jeramiah Howard, attributed her death to the heat.