Official commemorations are underway to commemorate 20 years since the 9/11 terror attacks against the United States of America.
The ceremony in New York started with a minute’s silence at 08:46 EST (13:46 BST) – the exact time the first plane hit the North Tower of the World Trade Center in 2001.
Thousands of people across the US have gathered to mark the sombre occasion.
Three presidents and their wives stood somberly side by side at the National September 11 Memorial, sharing a moment of silence to mark the anniversary of the nation’s worst terror attack with a display of unity.
Presidents Joe Biden, Barack Obama and Bill Clinton all gathered at the site where the World Trade Center towers fell two decades ago. They each wore blue ribbons and held their hands over their hearts as a procession marched a flag through the memorial, watched by hundreds of Americans gathered for the remembrance, some carrying photos of loved ones lost in the attacks.
Before the event began, a jet flew overhead in an eerie echo of the attacks, drawing a glance from Biden toward the sky.
Biden was a senator when hijackers commandeered four planes and executed the attack. Now he marks the 9/11 anniversary for the first time as commander in chief.
President Biden travelled to all three attack sites on Saturday – New York, Pennsylvania and Virginia.
A minute’s silence also marked the moment the second plane crashed into the South Tower of the World Trade Center. Similar tributes will take place at the times when a third jet struck the Pentagon in Virginia, a fourth hijacked plane crashed into a field in Pennsylvania, and finally when the World Trade Center towers collapsed.
In total, 2,977 people died in the attacks, when al-Qaeda militants hijacked US passenger planes and crashed them.
The first person to start reading out the names of the victims was Mike Low, who lost his daughter in the attack.
Speaking solemnly, he thanked those who helped him and his family get through “the darkest days of our lives”.
Mr Low recalled the “grey and black world” of New York in the aftermath of the attack, and asked for 9/11 to be remembered “not as numbers or a date, but the faces of ordinary people”.
Relatives took turns to read names of victims, as well as emotional messages to their own loved ones who died.
Bruce Springsteen and Broadway actor Kelli O’Hara sang at the commemoration, but by tradition, no politicians spoke there. In a video released Friday night, Biden addressed the continuing pain of loss but also spotlighted what he called the “central lesson” of Sept. 11: “that at our most vulnerable … unity is our greatest strength.”
Earlier on Saturday, a vigil was held at the Fire Department of New York memorial wall – a 56-foot-long bronze wall that honours the 343 firefighters who died on the day of the attacks.
In total, 441 first responders died in the attacks, the largest loss of emergency personnel in American history.
“We honour all those who risked and gave their lives in the minutes, hours, months and years afterwards,” Mr Biden said in his speech on Friday.
The terror attack defined the presidency of George W. Bush, who was reading a book to Florida schoolchildren when the planes slammed into the World Trade Center. He spent that day being kept out of Washington for security reasons — a decision that then-Sen. Biden urged him to reconsider, the current president has written — and then delivered a brief, halting speech that night from the White House to a terrified nation.
Additional reporting from AP and BBC