The commemoration of the 18th anniversary of the September 11 terror attacks has begun at ground zero with a moment of silence and tolling bells.
Almost 3,000 people were killed that day and thousands more were injured.
Former U.S. President George W. Bush, commander in chief at the time of the 2001 attacks, is due at an afternoon wreath-laying at the Pentagon. The effects are visible from airport security checkpoints to Afghanistan, where the post-9/11 US invasion has become America's longest war.
Anniversary ceremonies will also be held across the country commemorating the almost 3,000 people who died when hijacked planes rammed into the twin towers of New York's World Trade Center and the Pentagon while a fourth crashed into a field near Shanksville, Pennsylvania.
Americans commemorated 9-11 with solemn remembrances and vows to "never forget" 18 years after the deadliest terror attacks on American soil. "The last time hearing those precious words, 'I love you, '" the president said. "We must never forget and never fail to honor the memory of those who were lost here, in New York City, and in Washington D.C".
"We're at 204 in just the FDNY alone, and the NYPD's at 241".
"We have to remember that they gave everything for this job, for their communities, for their families", said Lexington firefighter Michael Hurt.
Witness at Ground Zero, another exhibition available, draws on the more than 500 pictures that were captured by French photographer and video director Stephane Sednaoui. "I know that you're watching over us right now". That's what "some people" did.
President Trump and First Lady Melania Trump will lead a moment of silence at the White House at 8:40 a.m. ET, minutes before the first plane crashed into the Trade Center's north tower, before participating in an observance at the Pentagon. In what has become an annual tradition, relatives began reading out the long list of those who were killed, saying a few words about those who died, in a ceremony that takes nearly four hours. She called her uncle, Abul Chowdhury, a "proud Muslim-American man who lived his life with a carefree nature, a zeal for adventure and a tenacity which I emulate every single day".
The memorial was erected in the spring in honor of the firefighters, police officers, and others who died of 9/11-related toxins after the attack. Over 51,000 people have applied. The event will include moments of silence, marking when the Twin Towers were struck and fell, when the Pentagon was attacked, and when Flight 93 crashed in Pennsylvania.
After years of legislative gridlock, dwindling money in the fund and fervent activism by ailing first responders and their advocates, Congress this summer made sure the fund won't run dry.
September 11 has become known also as a day of service. People around the country continue to volunteer at food banks, schools, home-building projects, park cleanups and other charitable endeavors on and near the anniversary.