Saturday marks 20 years since the September 11 terror attacks.
A total of 2,977 people were killed in the attacks, making them the deadliest terrorist incidents in history.
Planned and carried out by Al-Qaeda, the attacks saw four planes being hijacked and targeted at prominent American landmarks.
Here is a timeline of how events took place on 11 September, 2001.
All the times are in Eastern Time - UK times were five hours ahead
9/11 timeline of events
7:59am - American Airlines Flight 11 takes off from Boston’s Logan International Airport for Los Angeles with five hijackers on board, along with 76 passengers and 11 crew members.
8:14am - United Airlines Flight 175, a Boeing 767 with 59 passengers and nine crew members aboard, takes off from Boston. The flight is also heading to Los Angeles.
8:19am - Crew members on Flight 11 alert that a hijacking is taking place. A passenger named Daniel Lewin is stabbed, becoming the first fatality of the attacks.
8:20am - American Airlines Flight 77 takes off from Dulles International Airport out of Washington DC. The Boeing 757 aircraft is headed to Los Angeles with 64 people aboard. Five more hijackers, 53 passengers and six crew members are on board.
8:24am - Hijacker Mohammed Atta makes the first of two accidental transmissions from Flight 11 to ground control.
8:40am - The Air National Guard is mobilised in Massachusetts, with two fighter planes located at Cape Cod’s Otis Air National Guard Base scrambled to tail Flight 11. The planes were not yet in the air when Flight 11 crashed into the North Tower.
8:41am - United Airlines Flight 93, a Boeing 757 with 44 people aboard, takes off from Newark International Airport en route to San Francisco. The flight was scheduled to depart at 8am.
8:46am - Flight 11 crashes into the North Tower of the World Trade Center in New York City. The plane crashed between floors 93 and 99 of the tower.
8:50am - President George Bush, who is in Florida on a school visit, is alerted. First assumptions were that the crash was an accident.
9:00am - An evacuation order is issued for the entire World Trade Center complex. A Flight 175 crew member alerts air traffic controllers to the hijacking of the aircraft.
9:03am - Flight 175 crashes in the South Tower of the World Trade Center. The plane struck between floors 77 and 85. The crash was broadcast live on TV.
9:24am - Authorities notified of suspected hijacking of Flight 77 after passengers and crew alerted family members on the ground.
9:30am - President Bush gives a speech saying “terrorism against our nation will not stand”.
9:37am - Hijackers crash Flight 77 into the western facade of the Pentagon in Washington DC, killing 59 aboard and 125 military and civilian personnel in the building.
9:42am - The Federal Aviation Administration grounds all flights.
9:45am - The White House and US Capitol are evacuated.
9:59am - The South Tower of the World Trade Center collapses
10:07am - Passengers and crew aboard hijacked Flight 93 attempt to retake the plane. Hijackers deliberately crash the plane into a field in Pennsylvania. All 40 passengers and crew aboard are killed.
10:28am - The World Trade Center’s North Tower collapses, 102 minutes after being struck by Flight 11.
11:02am - New York Mayor Rudy Giuliani orders the evacuation of Lower Manhattan.