21 photos that depict the horror of 9/11 attacks

Smoke covering New York following the attack on the Twin Towers. Nearly 3,000 people were killed and countless more injured in the terror attack, that forever transformed the United States. (AP)

Pedestrians in lower Manhattan watch smoke billow from New York's World Trade Center on Tuesday, Sept. 11, 2001. Most notably, the event set off the rapid deployment of US forces to Afghanistan, marking the beginning of the country’s longest war. (AP)

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

People cover their faces as they escape the collapse of New York's World Trade Center on Sept. 11, 2001. (AP)

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

Roughly within half an hour of the attack on the WTC, an American Airlines flight took off from Dulles International Airport. It crash landed on the western wing of the Pentagon, where the US State Dept of Defence is housed.

An Armed Officer comforts a Pentagon employee while giving her medical aid outside the Pentagon in Washington on Tuesday, Sept. 11, 2001. (AP)

Flames and smoke pour from a building at the Pentagon in Washington on Tuesday, Sept. 11, 2001. The United States government blamed Al Qaeda chief Osama bin Laden as the mastermind behind the 9/11 attacks. Shortly after, US bombed Afghanistan. (AP)

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. (AP)

Two women hold each other as they watch the World Trade Center burn in New York Tuesday, Sept. 11, 2001. An estimated 33,000 or more people evacuated on that day from the World Trade Center and Pentagon. (AP)

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

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

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. (AP)

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

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

A person falls from the north tower of New York's World Trade Center as another clings to the outside, left, while smoke and fire billow from the building, Tuesday Sept. 11, 2001. (AP)

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

A survivor of the 9/11 attacks on the World Trade Center, looks at photos of those who perished, in a display at the 9/11 Tribute Museum, Friday, Aug. 6, 2021, in New York. (AP)

Student at the 9/11 Tribute Museum in New York City, US, August 26, 2021. (Reuters)

A docent at the 9/11 Tribute Museum holds an archival photograph of the twin towers in New York City, US, August 6, 2021. (Reuters)