Ceremonies will be held in New York City, Virginia and Pennsylvania.
NEW YORK -- 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 in Shanksville, Pennsylvania.
Another 9,000 people have died from 9/11-related illnesses over the last 25 years.
Victims' families, first responders and politicians will gather on Friday for annual remembrance ceremonies as Americans across the country pause to remember and reflect.
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.
President Donald Trump and first lady Melania Trump have arrived at the Pentagon in Virginia. Trump is expected to deliver remarks during the ceremony.
The third bell tolled at 9:37 a.m., which is the time American Airlines Flight 77 crashed into the Pentagon.
