How many people died in the 9/11 World Trade Center terror attack?

(FILES) In this file photo taken on September 11, 2001, a hijacked commercial aircraft approaches the twin towers of the World Trade Center shortly before crashing into the landmark skyscraper in New York. The remains of two more victims of 9/11 have been identified, thanks to advanced DNA technology, New York officials announced on September 8, 2021, just days before the 20th anniversary of the attacks. The office of the city's chief medical examiner said it had formally identified the 1,646th and 1,647th victim of the al-Qaeda attacks on New York's Twin Towers which killed 2,753 people. They are the first identifications of victims from the collapse of the World Trade Center since October 2019. / AFP / SETH MCALLISTER
This year marks the 20th anniversary of the 9/11 World Trade Center attacks. (AFP)

This year marks the 20th anniversary of the 9/11 attacks, which saw terrorists take control of planes over the US and turn them into deadly weapons.

Shortly before 9am, New York was turned into a scene of devastation after two planes smashed into the World Trade Center buildings.

In the 20 years since the attacks, the skyline of New York has changed, wars have been waged and Khalid Sheikh Mohammed – the principal architect behind the plot – has been captured and detained.

Terrorists also attacked the Pentagon in Washington DC, while those on board United 93 were thought to have been targeting either the White House or the Capitol before passengers decided to act and the plane came down before it reached the US capital.

But it was the images from the World Trade Center that are the most closely associated with a day that will never be forgotten.

The world trade center is seen in the New York City skyline. (Library of Congress/Carol M. Highsmith)
The World Trade Center was one of the most recognisable parts of the Manhattan skyline. (Library of Congress)

When did 9/11 happen?

On Tuesday, 11 September 2001, 19 al-Qaeda terrorists boarded several planes with a mission to kill as many people as possible.

American Airlines Flight 11 was the first plane to reach its target, hitting the North Tower of the World Trade Center at 8.46am.

There were mixed reports as it was at first believed by some that a small private plane had hit the tower by accident but less than 20 minutes later, it was obvious that a terror attack was taking place as United Airlines Flight 175 smashed into the South Tower of the twin towers at 9.03am.

Watch: 9/11 terror attacks 20 years on

Away from New York, American Airlines Flight 77 crashed into the Pentagon at 9.37am, and authorities were alarmed about United Airlines Flight 93, which was not responding to air traffic control and had veered off course.

Orders had been given to shoot the plane down if necessary, with concerns that it was aiming to crash into the White House or the Capitol in Washington DC.

But the plane crashed on the ground near Shanksville, Pennsylvania, at 10.03am after passengers and crew attempted to seize control from hijackers before the terrorists rolled the plane over and flew it into the ground.

How many people died?

The 9/11 attacks remain the deadliest terrorist attack in history, resulting in a total of 2,977 deaths, while all 19 hijackers were also killed.

The vast majority of deaths occurred in New York, with 2,606 people killed either inside the World Trade Center or on the ground below.

(FILES) In this file photo taken on September 10, 2001, an emergency vehicle fights a fire at the Pentagon in Washington, DC, hours after a hijacked airplane crashed into the Pentagon.     The remains of two more victims of 9/11 have been identified, thanks to advanced DNA technology, New York officials announced on September 8, 2021, just days before the 20th anniversary of the attacks. The office of the city's chief medical examiner said it had formally identified the 1,646th and 1,647th victim of the al-Qaeda attacks on New York's Twin Towers which killed 2,753 people. They are the first identifications of victims from the collapse of the World Trade Center since October 2019. / AFP / STEPHEN JAFFE
An emergency vehicle fights a fire at the Pentagon in Washington, DC, hours after a hijacked airplane crashed into the Pentagon. (AFP)

At the Pentagon, 125 people were killed while all 39 civilians on board United 93 were killed when it crashed into a field.

Over 90 countries lost citizens in all the attacks, including 67 from the UK – the most non-US deaths in the 9/11 attacks.

Smoke rises behind investigators as they comb the crater left by the
crash of United Airlines flight 93 near Shanksville, Pennsylvania
September 12, 2001. Flight 93 is one of four planes that were hijacked
as part of a deadly and destructive terrorist plot against the U.S.
September 11. REUTERS/Tim Shaffer

TMS
Smoke rises behind investigators as they comb the crater left by the crash of United Airlines flight 93 near Shanksville, Pennsylvania. (Reuters)

Ground Zero

In the aftermath of 9/11, the World Trade Center site became known as Ground Zero, which stretched over an area of 14.6 acres.

The twin towers were one of the most recognisable building of the Manhattan skyline and the outline radically changed after the buildings fell.

An aerial view shows only a small portion of the crime scene where the World Trade Center collapsed following the Sept. 11 terrorist attack.  Surrounding buildings were heavily damaged by the debris and massive force of the falling twin towers.   (Photo Credit: U.S. Navy/Eric J. Tilford)
An aerial view shows only a small portion of the crime scene where the World Trade Center collapsed following 9/11. (Getty)
JERSEY CITY, NJ - SEPTEMBER 7: The setting sun reflects off the windows of One World Trade Center in New York City on September 7, 2021 as seen from Jersey City, New Jersey. (Photo by Gary Hershorn/Getty Images)
The setting sun reflects off the windows of One World Trade Center in New York City, build to replace the original buildings. (Getty)

Hundreds of thousands of tonnes of debris had to be cleared following the attacks, while it took years to identify victims from body parts discovered at the site.

Plans to rebuild the World Trade Center were put in place soon after 9/11 and 20 years later, several new structures have been put in place – the most visible being One World Trade Center, a 1,776 feet (541 metres) skyscraper that is the tallest building in the US.

AFGHANISTAN:An undated file picture shows Osama Bin Laden attending a meeting with a Kalashnikov on his lap in an undisclosed place inside Afghanistan. Bin Laden is reported to have been funding the Abu Sayyaf, who are currently holding over a dozen hostages in the southern Philippine island of Jolo, through a Islamic charity, the International Islamic Relief Organisation (IIRO) which he set up in 1992 with his brother-in-law Mohammad Jamal Khalifa as a front for funding extremist groups. Bin Laden, a wealthy Saudi dissident living in Afghanistan, is wanted by the United States for masterminding a terrorist attack on tow US embassies in east Africa in 1998 which killed 224 people. AFP PHOTO/FILES (Photo credit should read AFP via Getty Images)
Osama Bin Laden attending a meeting with a Kalashnikov on his lap in an undisclosed place inside Afghanistan. (AFP/Getty)

Osama Bin Laden

While Khalid Sheikh Mohammed is regarded as the principal architect of the 9/11 attacks, it is al-Qaeda leader Osama Bin Laden who is most widely identified with the plot.

After becoming president in 1992, Bill Clinton made capturing Bin Laden a priority for the US following a series of attacks on US citizens at home and abroad.

However, it was 9/11 that ramped up the search to find him and a $25m reward was offered for information that led to the capture or killing of the terrorist leader.

A week after the 9-11 terrorist attack on the Twin Towers and the Pentagon, front pages of Newsday and the New York Daily News with the faces of Osama bin Laden and a cowboy-era outlaw's headline of 'Dead or Alive', on 18th September 2001, New York, USA. (Photo by Richard Baker / In Pictures via Getty Images Images)
A week after the 9/11 terrorist attacks, front pages of Newsday and the New York Daily News with the faces of Osama bin Laden and 'Wanted' headlines. (Getty)

Bin Laden’s whereabouts were a subject of confusion, with reports of him hiding out in mountains in caves in Afghanistan proving not to be fruitful, while it was also claimed he was attempting to avoid capture in neighbouring Pakistan.

For years the searches turned up nothing but US intelligence agencies finally tracked him down to a secure compound in Abbottabad, Pakistan, in 2011.

The house was raided by SEAL Team Six on 2 May, 2011, and Bin Laden was killed inside – nearly 10 years after the 9/11 attacks took place.

Watch: 9/11 survivor recounts remarkable escape from World Trade Center