The iconic World Trade Centre in the United States twin towers were reduced to rubble on September 11, 2001. The day, widely known as 9/11, changed everything for America and the world. The 9/11 attack left almost 3,000 people left and remain one of the deadliest attacks in world history.

This year, September 11 marks the 20th anniversary of the 9/11 attacks. As people remember the event and honours the families of those lost, here’s how the 9/11 terror attack unfolded on September 11, 2001, at the World Trade Center, the Pentagon, and on Flight 93 in Shanksville, Pennsylvania.

5.45 am – Reportedly, hijackers go past the security in Portland, Maine and board a flight to Boston. They connect to American Airlines Flight 11 there.

6.00 am – As September 11 was a primary election day in New York City, polling stations opened.

7.59 am – Flight 11 takes off from Boston for Los Angeles. On board were 11 crew members, 76 passengers, and five hijackers.

8.15 am – Flight 175 takes off from Boston for Los Angeles. On board were nine crew members, 51 passengers, and five hijackers.

8.19 am – Ground personnel was alerted by flight 11 crew members that a hijacking is underway. Officials believe that Daniel Lewin was the first victim of the attacks. It is thought that he may have tried to stop the hijackers but failed.

8.20 am – American Airlines Flight 77 takes off from Washington for Los Angeles. On board were six crew members, 53 passengers and five hijackers.

8.24 am – Trying to communicate with the passengers, a hijacker unknowingly contacts the air traffic control.

8.37 am – After which, Boston air traffic control alerts the military. Air National Guard jets in Massachusetts are mobilised to follow Flight 11.

8.42 am – United Airlines Flight 93 takes off from Newark for San Francisco. On board were seven crew members, 33 passengers, and four hijackers.

8.46 am – Flight 11 rams into floors 93 through 99 of the North Tower.

8.50 am – President George W. Bush is alerted. However, his advisors believe that this is a tragic accident.

8.55 am – The South Tower is declared secure.

8.59 am – Evacuation of both towers were ordered. A minute later, the order is expanded to the entire World Trade Center complex.

9.00 am – A Flight 175 alerts that a hijacking is underway.

9.03 am – Flight 175 crashes into floors 77 through 85 of the South Tower.

9.05 am – President Bush is alerted of the second crash. 25 minutes later he addresses Americans, saying that “terrorism against our nation will not stand.”

9.05 am – Flight 77 passenger Barbara Olson dials her husband, US Solicitor General Theodore Olson. He alerts other federal officials.

9.36 am – Secret Service agents secure Vice President Dick Cheney.

9.37 am – American Airlines Flight 77 crashes into the Pentagon. 59 people were killed on the plane and 125 on the ground.

9.42 am – The FAA grounds all flights.

9.45 am – The White House and US Capitol are evacuated.

9.59 am – The South Tower falls in 10 seconds after burning for 56 minutes. More than 800 people were killed in the accident.

10.03 am – United Airlines Flight 93 crashes near Shanksville, Pennsylvania. 40 people on board, excluding the hijackers, die.

10.15 am – The Pentagon’s outer ring collapses.

10.28 am – After burning for 102 minutes, the North Tower collapses, killing more than 1,600.

10.50 am – Five levels of the Pentagon’s west side collapse due to the fire.

11.02 am – Lower Manhattan evacuation is ordered by New York City Mayor Rudy Giuliani.

12.16 pm – The last flight still in the air above the continental United States lands.

12.30 pm – 14 people emerge from the North Tower stairwell rubble.

3.00 pm – Another survivor is rescued from the North Tower rubble.

5.20 pm – After burning for several hours, 7 World Trade Center collapses.

8.30 pm – President Bush, in an address, says that search is underway for the “those who are behind these evil acts.”

10.30 pm – Two PAPD officers are rescued from the debris of the World Trade Center.