Hundreds of thousands of people are expected to converge in the heart of Washington, where US President Donald Trump will host an Independence Day fireworks display and military flyover, while protesters will march for racial equality.
Disregarding the Washington mayor's warnings of the risk of gathering as many US states mark a record number of new Covid-19 cases, crowds began to assemble early on a hot Saturday morning.
The White House has invited hundreds of medics to the 4 July party - medics who have been treating Covid-19 patients. The fight against the pandemic is a theme of what the White House calls its Independence Day "Salute to America".
The US Department of the Interior plans to hand out 300,000 face masks to spectators who gather on the National Mall. They will also be urged to keep 1.8m apart.
Police officers blocked off streets around the White House, Black Lives Matter Plaza and the Lincoln Memorial, where demonstrators planned to join one of the dozen organised protests in advance of Trump's night-time address on the South Lawn.
Activist groups pledged to hold peaceful protests for reforms following the May killing of George Floyd, a 46-year-old black man who died after a white Minneapolis police officer knelt on his neck for nearly nine minutes.
Millions of Americans responded in June by marching against police brutality and racial inequality, leading to widespread removal of Confederate statues and other symbols of America's legacy of slavery.
Trump's Fourth of July event follows a night speech at Mount Rushmore in South Dakota yesterday where he accused "angry mobs" of trying to erase history and used the speech to paint himself as a bulwark against left-wing extremism.
Joe Biden, Trump's Democratic rival in the November election, struck a contrasting note with the Republican president and accused him in a Fourth of July op-ed of finding every day "new ways to tarnish and dismantle our democracy".
"We have a chance now to give the marginalised, the demonised, the isolated, the oppressed, a full share of the American dream," Biden said in a separate letter to donors.
Firework displays are a traditional highlight of 4 July, but an estimated 80 percent of cities and towns have cancelled their shows.
New York City usually holds an hour-long extravaganza, but this year it was replaced by five-minute displays through the week, organised by Macy's department store, with a final televised one today - all at undisclosed locations.
Beaches have been closed in Florida and California, city parades cancelled and firework displays curtailed.
Major League Baseball cancelled its 2020 All-Star Game for the first time since World War II.
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In his Mount Rushmore speech, Trump made little mention of the pandemic that has hit his re-election hopes, even as Covid-19 moved further into Trump's inner circle. Kimberly Guilfoyle, a senior campaign official and the girlfriend of Donald Trump Jr, tested positive in South Dakota before the event.
Washington Mayor Muriel Bowser had tried to dissuade the Trump administration from holding the fireworks display over the National Mall and informed the Department of the Interior that it went against health officials' guidance amid the pandemic.
Apart from fireworks spectators, activists of different stripes also appeared willing to disregard the health warnings.
Roar of the Deplorables, a bikers group, said via social media that they, too, were planning to gather in Washington on Saturday (US time) to stand in protest against what they call "the anti-Trump regime" and to celebrate the nation's birthday.
Freedom Fighters DC, a new activist group which seeks to rally an ethnically diverse generation of supporters behind liberty for all people, especially the black population of Washington, is one of the anti-racism groups ignoring the mayor's heed to refrain from gathering.
"Black folks are not free from the chains of oppression, so we don't get to truly celebrate Independence Day," said Kerrigan Williams, 22, one of the founders of the group, which will host a march and an arts demonstration.
"We're marching today to showcase that Black folks are still fighting for the simple liberties that the constitution is said to provide."
- Reuters / BBC