Often described as the worst terrorist attack in history, the trauma of 9/11 is still felt keenly by many 20 years on.
Images showing the horrifying events unfolding – as first one and then a second hijacked plane hit the World Trade Centre, another struck the Pentagon and a fourth crash-landed in a Pennsylvania field – have lost none of their impact over time.
Perhaps those showing the human cost of the day, in which almost 3,000 died, are more poignant still – the fear on the faces of those fleeing for their lives, the exhaustion of the rescue workers battling to save whoever they could and the despair of those searching for missing loved ones.
These pictures, viewed by millions around the globe in the aftermath of the attacks, led many to realise it had been a day that would change the course of history, not just for Americans, but for the world.
People hang from the windows of the North Tower
(Primera Hora/Getty)
US President George W Bush listens as White House Chief of Staff Andrew Card informs him of a second plane hitting the World Trade Center. Bush was conducting a reading seminar at the Emma E Booker Elementary School, in Sarasota, Florida
(Reuters)
Hijacked United Airlines Flight 175 flies towards the South Tower
(Reuters)
People run from the collapse of one of the Twin Towers
(AP)
People look down the street at the World Trade Center in flames
(Getty)
The South Tower is hit, becoming engulfed in flames
(Getty)
People run away as the North Tower collapses
(Getty)
A man covered in dust walks in the street near the World Trade Center Towers
(Reuters)
A man stands in the rubble, and calls out asking if anyone needs help, after the collapse of the first of the Twin Towers
(AFP/Getty)
Emergency vehicles stand before a damaged wall of the Pentagon
(AFP/Getty)
Tower 2 dissolves in a cloud of dust and debris about half an hour after the first Twin Tower collapsed
(Reuters)
People flee Lower Manhattan across the Brooklyn Bridge
(AP)
Firefighter Gerard McGibbon, of Engine 283 in Brownsville, Brooklyn, prays after the buildings collapsed
(Getty)
Marcy Borders stands covered in dust as she takes refuge in an office building following the collapse of the Twin Towers
(AFP/Getty)
An ambulance, covered with debris and on fire, after the collapse of the first tower
(AFP/Getty)
An American flag is posted in the rubble of the World Trade Centre as firemen and rescue workers clear the debris
(EPA)
Thick smoke billows into the sky from the area behind the Statue of Liberty
(AP)
Survivor Edward Fine, who was on the 79th floor of the North Tower when it was struck, covers his mouth as he walks through the debris
(AFP/Getty)
A rescue worker is pulled from the rubble
(Getty)
An unidentified New York City firefighter walks away after the collapse of the Twin Towers
(Getty)
Two people wear posters of a missing woman as they seek information following the attack on the World Trade Centre
(EPA)
Workmen begin the task of dismantling the destroyed remains World Trade Centre building
(EPA)
The Winter Garden surrounded by debris. Buildings nearby were heavily damaged by the falling twin towers
(AP)
Pedestrians look at photos of missing police and fire personnel missing a couple of weeks after the attacks
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The damaged area of the Pentagon building
(Reuters)
New Yorkers set up a monument and a candlelight vigil to commemorate the missing
(Getty)
NYPD police officer Ken Radigan rubs his eyes after briefly sleeping in a pew at St Paul’s Episcopal Chapel, near the site of the World Trade Center attack. The chapel served as a relief area for rescue workers
(Getty)
An aerial view of the remains of the World Trade Centre, more than two weeks after the attacks
(US Coast Guard via Reuters)
Firefighter Tony James cries while attending the funeral service for New York Fire Department Chaplain Rev Mychal Judge, in front of the St Francis of Assisi Church on 15 September, 2001. Judge died while giving the last rites to a fireman in the collapse of the World Trade Centre
(Getty)
