20 images that documented the enormity of 9/11 terror attack

It was a day of indelible images - apocalyptic, surreal, violent, ghostly, both monumental and profoundly personal. Wrenching to remember. Impossible to forget. The terrorist attacks of 9/11 were captured in countless pictures by news photographers, bystanders, first responders, security cameras, FBI agents and others. Even an astronaut on the International Space Station took some.

Twenty years later, The Associated Press has curated 20 of its photographers' frames from Sept. 11, 2001, when hijackers used commercial planes as missiles and crashed into New York's World Trade Center, the Pentagon and a Pennsylvania field. The attacks killed nearly 3,000 people and toppled the trade center's 110-story twin towers.

These photos document the enormity, chaos and emotion of 9/11 on every scale, from panoramic views of smoke rising over New York's skyline to a close-up of the anxious, smudged face of a woman hastening down a street blanketed with ashen dust.

Street scenes chart escalating horror as people stare and weep at the burning skyscrapers, then run from the dust cloud billowing through lower Manhattan after one of them crumbles. | People cover their faces as they escape the collapse of New York’s World Trade Center on Sept. 11, 2001.

A falling human form, almost silhouetted against one of the trade center towers, shows one of the most agonizing horrors of all.

Flames shoot from the windows of the Pentagon, a global symbol of military might that proved vulnerable to an attack by a handful of Islamic militants.

Deputy chief of the Army Reserve, Col. Malcolm Bruce Westcott, comforts Pentagon employee Racquel Kelley while giving her medical aid outside the Pentagon on Sept. 11, 2001. | Some show more intimate views of pain, but also humanity — an injured firefighter’s screaming face; a woman walking through the eerie blizzard of trade center debris with her arm around someone else’s shoulder; the then-deputy chief of the Army Reserve, Col. Malcolm Bruce Westcott, holding a comforting hand to Pentagon employee Racquel Kelley's brow while giving her medical aid. There are images of determination, including firefighters working amid the smoky rubble and a shopkeeper sweeping up the dust of catastrophe.

Fire and smoke billows from the north tower of New York's World Trade Center on Tuesday, Sept. 11, 2001.

People flee the falling South Tower of the World Trade Center on Tuesday, September 11, 2001.

Smoke billows through buildings in Manhattan as seen from Brooklyn after the collapse of New York’s World Trade Center, Tuesday, Sept. 11, 2001.

Pedestrians flee the area of New York’s World Trade Center in lower Manhattan on Tuesday, Sept. 11, 2001.

Harry Shasho sweeps up before being evacuated from his vitamin store after the collapse of New York’s World Trade Center on Tuesday, Sept. 11, 2001

Two women hold each other as they watch the World Trade Center burn in New York Tuesday, Sept. 11, 2001.

Smoke billows from one of the towers of the World Trade Center as flames and debris explode from the second tower, Tuesday, Sept. 11, 2001.

People walk over New York's Brooklyn Bridge from Manhattan to Brooklyn following the collapse of both World Trade Center towers on Sept. 11, 2001

People flee the scene near New York's World Trade Center Tuesday, Sept. 11, 2001.

A fireman screams in pain as he is rescued shortly after both towers of New York's World Trade Center collapsed following a terrorist attack, Tuesday, Sept. 11, 2001.

Firefighters work beneath the destroyed mullions, the vertical struts, of the World Trade Center in New York on Tuesday, Sept. 11, 2001.

A firefighter moves through piles of debris at the site of the World Trade Center in New York, Tuesday, Sept. 11, 2001.

The remains of the World Trade Center stands amid the debris in New York, Tuesday, Sept. 11, 2001.

Finally, as night falls, people gaze across New York Harbor at the smoke, trying to make sense of what happened in front of their eyes. As we still are today.