President Donald Trump and Biden are also due to visit Shanksville separately later in the day
Democratic presidential candidate Joe Biden, Vice President Mike Pence, and New York Governor Andrew Cuomo, all masked, joined New York's somber 19th anniversary of the September 11 attacks at the site of the destroyed World Trade Centre.
Biden and Pence, both masked, bumped elbows in greeting, one of the many ways the anniversary ceremony has been changed by the coronavirus pandemic, which has killed more than 196,000 people in the United States.
About 200 people joined the New York ceremony, where the names were read out of the nearly 3,000 people killed when two hijacked jets slammed into the Twin Towers, with a third hitting the Pentagon and a fourth taken down in Shanksville, Pennsylvania, when its passengers rose up against the al Qaeda hijackers.
President Donald Trump and Biden are also due to visit Shanksville separately later in the day.
Prior to boarding a plane from his Delaware home, Biden pledged not to make any news during the solemn day.
"I'm not going to talk about anything other than 9/11. We took all our advertising down. It's a solemn day, and that's how we're going to keep it, okay?," Biden said.
The sun struggled to pierce hazy clouds in New York, a contrast with the 2001 morning of the attacks, which people present that day remember for its piercing, clear skies.
Trump left the White House to attend a morning ceremony at the Flight 93 National Memorial in Shanksville, a White House official said.
The event, in remembrance of the 40 passengers and crew who died when the plane plunged into a field after they struggled with the hijackers, will be closed to the public because of coronavirus concerns, the National Park Service said.
Later in the day, the Bidens will visit the Shanksville site to pay their respects to the victims. The two candidates are not expected to cross paths in Pennsylvania, a battleground state that is vital to the November 3 election between Trump and Biden.
Flight 93, bound for San Francisco from Newark, New Jersey, never hit its intended target — the four hijackers were believed to be planning to crash it into either the U.S. Capitol or the White House — after passengers stormed the cockpit and attempted to regain control of the aircraft.
The ceremonies marking the attacks are a regular stop for presidential candidates and officials. Trump visited Shanksville for the 9/11 anniversary in 2018, and has attended memorial ceremonies at the Pentagon.
Biden went to memorials in Shanksville during his years as vice president under Barack Obama.
During the 2016 presidential campaign, Trump and Democratic presidential candidate Hillary Clinton both visited the Ground Zero memorial in New York.
Biden's campaign said it was pulling its television ads off the air on Friday.