(All timings are EDT)
7:58 am: United Airlines Flight 175, a Boeing 767, leaves Boston's Logan airport for Los Angeles with 56 passengers and 9 crew.
7:59 am: American Airlines Flight 11, a Boeing 767, also departs Boston bound for Los Angeles with 81 passengers and 11 crew.
8:01 am: United Airlines Flight 93, a Boeing 757, leaves Newark for San Francisco with 38 passengers and 7 crew.
8:10 am: American Airlines Flight 77, a Boeing 757 departs Washington's Dulles airport for Los Angeles with 58 passengers and 6 crew.
8:45 a.m: American Airlines Flight 11 crashes into the North Tower of the World Trade Center in New York.
9:03 am: News cameras trained on the burning tower capture live United Airlines Flight 175 crashing into the South Tower of the WTC causing a devastating explosion.
9:10 am: In Florida President George W. Bush is reading to children in a classroom when the Chief of Staff, Andrew Card, whispers news of the attacks into his ear.
9:17 am: The FAA shuts down all New York City area airports.
9:20 am: The FBI announces that it is investigating reports of planes being hijacked.
9:30 am: President Bush, speaking in Florida, says the country has suffered an "apparent terrorist attack."
9:38 am: American Airlines Flight 77 crashes into the west side of the Pentagon, sending up a huge plume of smoke. Evacuation begins immediately.
9:40 am: The FAA halts all flight operations at U.S. airports, the first time in U.S. history that air traffic nationwide has been halted.
9:45 am: The White House and the Capitol are evacuated amid further threats.
9:50 am: The South Tower of the WTC collapses sending a massive pall of smoke across Manhattan. Many emergency workers and firefighters are crushed or trapped as well as those who could not get out of the tower.
9:58 am: An emergency dispatcher in Pennsylvania receives a call from a passenger on United Airlines Flight 93 who says: "We are being hijacked, we are being hijacked."
10:00 am: United Airlines Flight 93 crashes 130 km south-east of Pittsburgh.
10:08 am: Secret Service agents armed with automatic rifles are deployed into Lafayette Park across from the White House.
10:10 am: A portion of the Pentagon collapses.
10:13 am: The United Nations building evacuates, including 4,700 people from the headquarters building and 7,000 total from UNICEF and U.N. development programmes.
10:22 am: In Washington, the State and Justice Departments are evacuated, along with the World Bank. 10:24 am: The FAA reports that all inbound trans-Atlantic aircraft flying into the United States are being diverted to Canada.
10:25 am: A car bomb is reported to have exploded outside the State Department in Washington.
10:28 am: The WTC's North Tower collapses, releasing a tremendous cloud of debris and smoke.
10:45 am: All federal office buildings in Washington are evacuated.
10.46 am: U.S. Secretary of State Colin Powell cuts short his trip to Latin America to return home.
10.48 am: Police confirm the crash in Pennsylvania.
10:53 am: New York's primary elections scheduled for today are postponed.
10:54 am: Israel evacuates all diplomatic missions.
10:57 am: New York Governor George Pataki says all state government offices are closed.
11:02 am: New York Mayor Rudolph Giuliani urges New Yorkers to stay at home and orders an evacuation of the area south of Canal Street.
11:18 am: American Airlines confirms it has lost two aircraft.
11:26 am: United Airlines confirms Flight 93 has crashed in Pennsylvania, south-east of Pittsburgh.
12:04 pm: Los Angeles International Airport is evacuated.
12:15 pm: San Francisco International Airport is evacuated and shut down.
12:15 pm: The Immigration and Naturalization Service says U.S. borders with Canada and Mexico are on the highest state of alert, but no decision has been made about closing borders.
12:30 pm: The FAA says 50 flights are in U.S. airspace, but none are reporting any problems.
12:39 pm: President Bush, speaking from Barksdale Air Force Base in Louisiana, says that all appropriate security measures are being taken, including putting the U.S. military on high alert worldwide. He asks for prayers for those killed or wounded in the attacks and says: "Make no mistake, the United States will hunt down and punish those responsible for these cowardly acts."
1:20 pm: President Bush leaves Barksdale Air Force Base and flies to Omutt Air Force Base in Nebraska.
1:27 pm: A state of emergency is declared in Washington DC by Mayor Anthony Williams.
1:44 pm: The Pentagon says five warships and two aircraft carriers leave the U.S. Naval Station in Norfolk, Virginia, to protect the East Coast from further attack and to reduce the number of ships in port. The two carriers, the USS George Washington and the USS John F. Kennedy, head for the New York coast. The other ships are frigates and guided missile destroyers capable of shooting down aircraft.
2:30 pm: The FAA announces there will be no U.S. commercial air traffic until noon EDT Wednesday.
2:48 pm: At a news conference, Giuliani says that subway and bus service are restored in New York City. Asked about the number of people killed, Giuliani says, "I don't think we want to speculate about that -- more than any of us can bear."
3:55 pm: Karen Hughes, a White House counsellor, says the President is at an undisclosed location, later revealed to be Omutt Air Force base in Nebraska, and is conducting a National Security Council meeting by phone. Vice President Dick Cheney and National Security Adviser Condoleezza Rice are in a security facility at the White House. Defence Secretary Donald Rumsfeld is at the Pentagon.
3:55 pm: Giuliani now says the number of critically injured in New York City is up to 200 with 2,100 total injuries reported.
4:06 pm: California Governor Gray Davis dispatches urban search-and-rescue teams to New York City.
4:10 pm: Building 7 of the WTC complex is reported on fire.
4:20 pm: U.S. Senator Bob Graham, chairman of the Senate Intelligence Committee, says he is "not surprised there was an attack (but) is surprised at the specificity." He says he is "shocked at what actually happened -- the extent of it."
4:25 pm: The American Stock Exchange, the Nasdaq and the New York Stock Exchange say they will remain closed on Wednesday.
4:30 pm: The President leaves Omutt Air Force Base in Nebraska aboard Air Force One to return to Washington
5:20 pm: The 47-story Building 7 of the WTC complex collapses. The evacuated building was damaged when the twin towers collapsed. Other nearby buildings in the area remain ablaze.
5:30 pm: U.S. officials say the plane that crashed in Pennsylvania could have been headed for one of three possible targets: Camp David, the White House or the Capitol building.
6 pm: Explosions are heard in Kabul, Afghanistan, hours after the attacks in the United States. The attacks occur at 2:30 am local time. Afghanistan is home of Saudi militant Osama bin Laden, who U.S. officials say is behind the deadly attacks. Officials say later that the United States has no involvement in the incident whatsoever.
6:10 pm: Mayor Giuliani urges New Yorkers to stay home on Wednesday if they can.
6:40 pm: U.S. Defence Secretary Donald Rumsfeld holds a news conference in the Pentagon, noting the building is operational. "It will be in business tomorrow," he says.
6:54 pm: Bush arrives back at the White House and is scheduled to address the nation at 8:30 p.m. The President earlier lands at Andrews Air Force Base with a three-fighter jet escort.
7:45 pm: The New York Police Department says that at least 78 officers are missing. The city also says that as many as half of the first 400 firefighters on the scene are believed to be killed.
8:30 pm: President Bush addresses the nation, saying "thousands of lives were suddenly ended by evil" and asks for prayers for the families and friends of the victims. "These acts shatter steel, but they cannot dent the steel of American resolve," he says. The President says the U.S. government will make no distinction between the terrorists who committed the acts and those who harbour them. He adds that government offices in Washington are reopening for essential personnel on Tuesday night and for all workers on Wednesday.