Six moments of silence were held Saturday to mark the times of the 9/11 attacks as President Joe Biden and other leaders honored the heroes and remembered those who tragically died 20 years ago on one of America's darkest days.
Biden and first lady Jill Biden joined a large crowd including victims' families at the National September 11 Memorial and Museum, where the twin towers once stood, to observe the first at 8:46 a.m. ET.
That marked the time Al Qaeda terrorists crashed American Airlines Flight 11 into the north tower of New York's World Trade Center two decades ago.
They were joined by former Presidents Barack Obama and Bill Clinton as well as several national and state leaders, members of the emergency services and large crowds.
Just 17 minutes later, a second moment of silence was held to mark the time when United Airlines Flight 175 hit the south tower.
After both moments, family members read out the names of those killed in the 9/11 attacks and the 1993 World Trade Center bombing. Bruce Springsteen also performed "I'll See You in My Dreams."
Meanwhile at the Pentagon, the first of a number of events began shortly before 7 a.m. ET. As the national anthem rang out, a flag was unfurled down the side of the building, which was hit that day.
A third moment of silence was held at 9:37 a.m. ET, to remember those who lost their lives when American Airlines Flight 77 crashed into the Pentagon. Afterward, a rendition of "You’ll Never Walk Alone" was performed for the crowd followed by more names of those who died being read.
Download the NBC News app for breaking news and politics
More moments of silence were held to mark when the south tower collapsed at 9:59 a.m. ET and when the neighboring north tower crumbled to the ground at 10:28 a.m.
Outside Shanksville, Pennsylvania, a moment of silence was held at 10:03 a.m. ET for the heroic passengers who fought terrorists aboard United Airlines Flight 93 and prevented the plane from reaching Washington.
Family members read the names of their loved ones as a bell rang.
"Twenty years ago, we all found in different ways, in different places, but all at the same moment, that our lives would be changed forever. The world was loud with carnage and sirens, and then quiet with missing voices that would never be heard again," he said. "These lives remain precious to our country and infinitely precious to many of you. Today we remember your loss, we share your sorrow and we honor the men and women you have loved for so long and so well."
Bush went on to say the “actions of an enemy revealed the spirit of a people.”
"In these memories, the passengers and crew of Flight 93 must always have an honored place. Here the intended targets became the instruments of rescue, and many who are now alive owe a vast, unconscious debt to the defiance displayed in the skies above this field," he said.
Vice President Kamala Harris gave remarks around 10:45 a.m. ET.
"We stand today with all those who lost someone on Sept. 11, 2001, and in the aftermath of the attacks," she said. "So many in our nation, too many in our nation, have deeply felt the passage of time these last 20 years."
"We are gathered today on hallowed ground, at this place that has been sanctified by sacrifice to honor the heroism that the 40 passengers and crew members showed in the face of grave terrorism," Harris continued.
"The 40 passengers and crew members of Flight 93, as we all know, they didn’t know each other, most of them didn’t know each other. They were different people from different places," Harris said. "But they did not focus on what may separate us. ... In a matter of minutes, in the most dire of circumstances, the 40 responded as one.”
Biden arrived in New York on Friday night as the skyline was illuminated by the “Tribute in Light,” hauntingly marking where the towers once stood.
On Saturday afternoon, he joined several others to lay a wreath in the field where Flight 93 came down near Shanksville. He spoke about the difficulties of having memorials during a question-and-answer session at the Shanksville Volunteer Fire Department.
“These memorials are really important. But they’re also incredibly difficult for the people affected by them because it brings back the moment they got the phone call, it brings back the instant they got the news," the president said.
He went on to praise Bush's speech and talked about the nation coming together. “Are we going to, in the next four, five, six, 10 years, demonstrate that democracies can work, or not?” he asked.
He is the fourth president to console the nation on the anniversary of that dark day, one that has shaped many of the most consequential domestic and foreign policy decisions made by the chief executives over the past two decades.
He concluded official events just before 5 p.m. ET by laying a wreath at the Pentagon. Biden was joined by the first lady, Harris and her husband, Defense Secretary Lloyd Austin, and Joint Chiefs of Staff Chair Gen. Mark Milley.
Former President Donald Trump also gave remarks while meeting with police officers in New York City.
"It's a sad day. It's a very sad day for a lot of reasons," Trump said before referencing the U.S. withdrawing troops from Afghanistan to end a 20-year war. "And we just added to that reason last week. That should have never been allowed to happen. ... Very disappointing."
Trump then praised the work of the New York City Police Department before answering a few questions from officers and posing for pictures.
CORRECTION (Sept. 12, 2021, 6:55 p.m. ET): A previous version of this article misstated the airline of the plane that hit the south tower and the duration between the two crashes. United Airlines Flight 175, not American Airlines, hit the south tower 17 minutes, not 23 minutes, after the north tower was hit.