TWENTY years ago today, the world’s deadliest terrorist attack took place.

A series of incidents on the morning of September 11, 2001, claimed the lives of 2,996 people – including over 400 firefighters and police officers.

Carried out by the 19 members of the militant Islamist terrorist group al-Qaeda, the attack saw three buildings in the World Trade Center collapse.

The South Tower collapsed after 56 minutes of burning. The North Tower followed after burning for 102 minutes.

The rescue, recovery and clean-up of the 1.8 million tons of wreckage site took nine months.

With US times, here is a blow-by-blow account of what happened on that fateful day.

September 11, 2001

4am

Egyptian-born Mohamed Atta prepares to check out of the Milner Hotel in Boston.

In his luggage, he has a copy of the Quran, a knife, pepper spray and a videotape on how to fly Boeing jets.

The Argus: Then UK Prime Minister Tony Blair Then UK Prime Minister Tony Blair

6.30am

UK Prime Minister Tony Blair is on a train to Brighton with his press secretary Alastair Campbell.

The pair are putting together the finishing touches to the PM’s speech for the TUC conference.

6.45am

Mohamed Atta and four Saudi nationals check-in for Flight 11 – bound for Los Angeles from Boston’s Logan International Airport.

Because of their nationality and travel movements, three of the men are identified as potentially suspect and their bags x-rayed, but nothing suspicious is found.

7.30am

Saudi brothers Nawaf and Salem al Hazmi arrive at Washington Dulles Airport to catch American Airlines Flight 77.

Salem sets off the metal detectors. Security guards check him with a hand-wand, but it picks up nothing suspicious.

8.14am

Fifteen minutes into Flight 11’s journey, the hijack begins.

Atta and the other terrorists spray mace into the first-class cabin and force passengers to the rear of the plane.

Passenger Daniel Lewin attempts to intervene but is killed by one of the terrorists before the group force their way into the cockpit, where Atta takes over the controls.

8.45am

On United Airlines Flight 175, the hijackers storm the cockpit and kill the pilots.

8.46am

American Airlines Flight 11, loaded with 20,000 gallons of jet fuel, crashes into the North Tower of the World Trade Center at 460mph.

Hundreds are killed by the impact and more than 1,300 workers are trapped on the floors above.

The Argus: 9/11 was officially the world’s deadliest terrorist attack 9/11 was officially the world’s deadliest terrorist attack

8.49am

An advert on CNN is interrupted and live images of the burning building appear on screen.

The presenter says: “This just in, you’re obviously looking at some very disturbing live shots. Clearly something devastating happening there.”

8.50am

On Flight 77, the terrorists use box cutters to get into the cockpit and kill the crew.

Their target is the Pentagon.

8.57am

Hundreds of firefighters are on their way to the scene.

People stuck on the higher floors of the north tower begin to jump.

9am

Tony Blair is reading through his speech inside a room at the Grand Hotel in Brighton.

Alastair Campbell bursts into the room and insists that he switch on the television.

9.03am

United Airlines Flight 175 crashes into South Tower of the World Trade Center.

9.08am

US President George Bush is reading a book to a class of children at Emma Booker Elementary School in Florida.

White House chief of staff Andy Card enters the room and whispers in the president’s ear: “America is under attack”.

The Argus: Then US President George Bush at Emma Booker Elementary School in Florida Then US President George Bush at Emma Booker Elementary School in Florida

9.20am

President Bush delivers a hastily written statement.

“Ladies and gentlemen, this is a difficult day for America. Two aeroplanes have crashed into the World Trade Centre in an apparent attack on our country,” he said.

“Terrorism against our nation will not stand.”

9.28am

On Flight 93, four hijackers storm the cockpit.

Buildings across New York and the United States begin to be evacuated, including the Empire State Building, Washington Monument and the Transamerica Pyramid in San Francisco.

9.37am

Flight 77 crashes into the west wall of Pentagon – killing a total of 189 people.

9.42am

For the first time in history, the FAA grounds all flights over or bound for the United States.

Around 3,300 commercial flights and 1,200 private planes are guided to land at airports in Canada and the US.

9.59am

The South Tower of the World Trade Center collapses.

10.03am

A fourth flight, United Airlines Flight 93, crashes in Pennsylvania, after passengers fought four hijackers.

The flight’s target is believed to have been the Capitol or the White House.

10.28am

The World Trade Center’s North Tower collapses - 102 minutes after being struck by Flight 11.

11am

Tony Blair made his way from his hotel to a conference centre in Brighton.

The decision was made to abandon his speech at the TUC conference.

After a few impromptu remarks to delegates, Blair took the first train back to London to meet his security chiefs.

2.51 pm

The US Navy dispatches missile destroyers to New York and Washington, D.C.

4pm

Tony Blair addresses the nation in a broadcast from Downing Street, promising that “we here in Britain stand shoulder to shoulder with our American friends”.

5.20pm

The 47-story seven World Trade Center collapses after burning for hours.

8.30pm

President Bush addresses the US, calling the attacks “evil, despicable acts of terror” and declaring that America, its friends and allies would “stand together to win the war against terrorism.”