Ceremonies are being held in New York City, Virginia and Pennsylvania.
Friday marks 25 years since the Sept. 11, 2001, terror attacks, which claimed the lives of 2,977 people at the World Trade Center, the Pentagon and Shanksville, Pennsylvania.
Another 9,000 people have died from 9/11-related illnesses over the last 25 years.
Victims' families, first responders and politicians are gathering for annual remembrance ceremonies at the memorials in downtown Manhattan, the Pentagon in Virginia, and Shanksville, as Americans across the country pause to remember and reflect.
"9/11 Tribute in Light: Live from Lower Manhattan," a one-hour ABC News multiplatform live special, premieres on Friday, Sept. 11, at 8:00 p.m. EDT across ABC, Disney+, Hulu, National Geographic, ABC Owned Television Stations livestreams and ABC News Live.
The president addressed the crowd at the 9/11 ceremony at the Pentagon.
Trump reflected on the horrors of the attack and the thousands killed in on 9/11, but noted the strong response from America against its enemies.
"That's why we fight today," he said. "We do not have a choice, we can only have victory."
The fifth moment of silence was held at 10:03 a.m., to mark the moment passengers on United Airlines Flight 93 fought back against the hijackers, resulting in the plane crashing into a field near Shanksville, Pennsylvania.
The reading of the names at the 9/11 Memorial & Museum ceremony was paused once again at 9:59 a.m., when the fourth bell tolled, marking the time the World Trade Center’s South Tower collapsed.
A moment of silence was held at the Pentagon at 9:37 a.m. when a plane struck the building.
The crowd listened intently as the names of all of those who were killed in the attack were read, and a bell was rung.
