Ceremonies were held Friday 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 gathered 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.
At 8:46 a.m., the first moment of silence was held at the ceremony at the 9/11 Memorial & Museum ceremony. This marks the time American Airlines Flight 11 crashed into the World Trade Center’s North Tower.
The New York City Fire Department lost 343 members at the World Trade Center. In the last 25 years, another 453 have died of 9/11-related illnesses, mainly cancer, from their service that day and during the immediate aftermath.
“It’s a heavy day for the fire department,” Commissioner Lillian Bonsignore told ABC News. “It’s not slowing down, unfortunately. We continue to live they day over and over again.”
The NYPD lost 23 members at the World Trade Center. In the last 25 years, another 469 have died of 9/11-related illnesses.
“We have to remember that the largest crime scene in the world very quickly became the largest race and recovery effort that this city certainly has ever seen,” Police Commissioner Jessica Tisch told ABC News.
She said the “vast majority” of officers working in 2001 are no longer with the department, which “makes it all the more important that we pass their legacies and stories down to the next generation.”
-ABC News' Aaron Katersky
President Donald Trump will attend the 9/11 ceremony at the Pentagon in Virginia and will not be at the New York City ceremony at ground zero, according to a White House official.
Vice President JD Vance will go to ground zero, an official said, adding that the three ceremonies at the Pentagon, ground zero and Shanksville, Pennsylvania, will all have administration officials in attendance.
Robert Schnelle remembers being the first member of the New York Police Department's K-9 Unit on the scene when the first plane struck the North Tower of the World Trade Center on Sept. 11.
Seventeen minutes later, Schnelle watched as a second plane struck the South Tower. Less than an hour later, Schnelle and his rescue dog, Atlas, hid for cover when the South Tower collapsed around them.
For the next eight months, Schnelle and Atlas remained there at what became ground zero, working 12-hour search-and-rescue shifts at the site of the deadliest terror attack in U.S. history.
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