Americans marked the nation's 250th Independence Day in the capital on Saturday amid extreme heat and a charged political atmosphere, as President Donald Trump addressed crowds at the National Mall ahead of a massive fireworks display delayed for hours by an incoming storm.

The event began after storms prompted a roughly two-hour evacuation of the National Mall just after 7 pm EDT.

Trump spoke to a large crowd inside a cordoned off area with heavy security, overlooked by the Washington Monument. Thousands more lined nearby streets, unable to get in.

During his speech, he spoke of iconic and challenging times in America's history and used flags such as one from Abraham Lincoln's casket and another that was on the plane with the Wright Brothers to illustrate his point.

Throughout the activities to mark the milestone in the nation's story, revelers across the East Coast battled extreme, brutally hot temperatures forecast at 90 degrees and which sizzled to heat indexes of over 110 to 115 degrees Fahrenheit or 43 to 46 degrees Celsius, the National Weather Service (NWS) said.

Gail, 75, from Virginia, who visited the White House during the Fourth of July weekend with her husband, son and daughter-in-law, explained that managing the extreme heat was "hard" but said it was even tougher on her husband.

Earlier on Saturday morning, the city's National Independence Day Parade, hosted by the National Park Service, was canceled due to an "Extreme Heat Warning" from NWS.

A scheduled rodeo was also called off because of the extreme heat. Local Metro stations were packed full of visitors. Organizers added water and cooling stations along with medical support at the fair to keep revelers cool.

Amid the party-like atmosphere, throngs of people in Washington were met by a heavy security presence, estimated to include thousands of law enforcement officers, agents and 5,000 National Guard troops along with military-style vehicles, the Associated Press reported.

The White House could barely be seen by visitors as it was barricaded behind high black metal gates.

Tensions were also high on the streets as dozens of members of the white nationalist group Patriot Front, wearing face masks and carrying Confederate battle flags, held a march. No arrests were reported, according to the Metropolitan Police Department, the AP reported on Saturday.

Meanwhile, in New York City, Vice-President JD Vance addressed sailors aboard the USS Kearsarge during the Sail4th 250 events.

"You will hear a couple of small but loud voices today speak obsessively, not of our national greatness, but of our national imperfections" he said. "Reject the view of your nation that sees only its sins, but not its grace and its greatness."

Amid the nation's 250th birthday, Americans also reflected on divisiveness in politics, as well as national pride.

"Well, our leaders need to get their act together and be able to just talk," Randy Tennant 78, from Syracuse, New York, told China Daily. "They don't talk now. They just argue. They put each other down, 25, 30 years ago, they used to talk together."

Only 4 in 10 American adults felt "proud" about the country's 250th anniversary, an April poll by The Associated Press-NORC Center for Public Affairs Research found.

According to the latest Gallup poll, only 46 percent of Americans believe everyone has an equal opportunity to achieve the American Dream.

"I would say America, 250 years old, is in a midlife crisis, for sure," Ryan Hilligoss, a New York resident, told China Daily. "With all the oligarchy that's going on, with the economics, the American Dream is very limited."

Other visitors expressed mixed feelings about the milestone, saying the anniversary offered an opportunity both to celebrate the country's achievements and to reflect on its economic and political challenges.

"I think the 250th year represents growth, different perspectives, divisiveness, all the above," Shuba Maniram, another New York resident, told China Daily.

Peter Christian, who lives in California, said two major problems confronting the country are widening wealth disparities and a growing unwillingness to compromise.

"Wealth disparity is causing a serious problem, and you have a lot of people who have taken a 'my way or the highway' attitude toward everything, and those two things are causing a lot of problems for the country," he said.