Updated from 3:21 p.m. EDT Tuesday

In what President Bush termed an "apparent terrorist attack" against the U.S., three aircraft slammed into American icons, two into the World Trade Center towers in New York and one into the Pentagon in Washington, D.C.

The attacks left Americans in fear of further terrorism and shook international markets, which worried about the economic ramifications of such widespread terrorism against a nation.

Here is a timeline of the events (EDT). Many times are approximate, based on eyewitness and news reports:

  • 8:51 a.m.: American Airlines jetliner crashes into 1 World Trade Center, the north tower.

  • 9:06 a.m.: United Airlines jet crashes into 2 World Trade Center, the south tower.

    American Airlines confirms Flight 11, a Boeing 767 aircraft, from Boston to Los Angeles with 92 passengers was one of the planes. United confirms that its Flight 175, also a Boeing 767 aircraft en route from Boston to Los Angeles with 56 passengers and nine crew members, was the plane that struck the south tower.

  • 9:17 a.m.: Federal Aviation Administration closes all New York City airports.

  • 9:30 a.m.: Trading at the New York Stock Exchange and other U.S. exchanges was suspended, prior to opening.

  • 9:30 a.m.: President Bush, speaking at an education appearance in Florida, says the U.S. has experienced an "apparent terrorist attack."

  • 9:35 a.m.: Port Authority of New York and New Jersey closes all bridges and tunnels in the New York City area.

  • 9:40 a.m.: Federal Aviation Administration orders all aircraft in domestic air space grounded. All international flights with U.S. destinations are diverted to Canadian airports.

  • 9.43 a.m.: Aircraft crashes into courtyard on the grounds of the Pentagon in Arlington, Va., outside Washington, D.C.

    It is later confirmed that the aircraft was American Flight 77, a Boeing 757 en route from Washington Dulles to Los Angeles with 58 passengers and six crew members.

  • 9:45 a.m.: White House evacuation ordered. Secret Service says "credible threat" received.

  • 9:57 a.m.: President Bush departs Florida for an unknown location, now known to be Barksdale Air Force Base in Shreveport, La.

  • 10.07 a.m.: The South Tower of the World Trade Center collapses.

  • 10:08 a.m.: Secret Service agents with automatic rifles sent to Lafayette Park across from the White House.

  • 10:10 a.m.: United Airlines flight 93, a Boeing 757 aircraft en route from Newark to San Francisco with 38 passengers, two pilots and five flight attendants crashes near Johnstown, Pa.

  • 10:13 a.m.: The United Nations building is evacuated.

  • 10:15 a.m.: A portion of the Pentagon collapses after the crash.

  • 10:19 a.m.: The Associated Press reports a car bomb attack at the State Department in Washington. At 10:50 a.m., the report is proved false.

  • 10:22 a.m.: The State and Justice departments and the World Bank are evacuated in Washington, D.C.

  • 10.28 a.m.: The North Tower of the World Trade Center collapses.

  • 10:45 a.m.: All federal office buildings in Washington are evacuated.

  • 10.46 a.m.: Secretary of State Colin Powell leaves Latin America trip early, returns to the U.S.

  • 10:50 a.m.: New York City's mayoral primary postponed.

  • 10:54 a.m.: Israel orders all diplomatic missions evacuated.

  • 12:04 p.m.: Los Angeles International Airport evacuated.

  • 12:15 p.m.: San Francisco International Airport evacuated.

  • 10:30 a.m.: Immigration and Naturalization Services place U.S. borders with Canada and Mexico at "highest alert." Borders remain open to limited traffic.

  • 12:30 p.m.: The FAA reports 50 planes remain in U.S. airspace and all are operating without problems or incident.

  • 1:04 p.m.: President Bush, now at Barksdale Air Force Base in Louisiana, says, "Freedom was attacked by a faceless coward ... and will be defended."

  • 1:27 p.m.: State of emergency declared in Washington, D.C.

  • 1:44 p.m.: Pentagon says seven vessels -- five warships and two aircraft carriers -- are leaving the U.S. Naval Station in Norfolk, Va. The two carriers, the USS George Washington and the USS John F. Kennedy will be off the New York coast. The other ships -- frigates and destroyers with guided missile capabilities -- will be stationed in undisclosed locations between Washington and New York.

  • 1:48 p.m.: President Bush leaves Barksdale Air Force Base for an undisclosed location, now known to be Offut Air Force Base in Omaha, Neb. Offut is home of the Strategic Air Command, a key strategic outpost during the Cold War era.

  • 2:30 p.m.: Federal Aviation Administration suspends all commercial air traffic until noon EDT Wednesday.

  • 2:49 p.m.: New York Mayor Giuliani says mass transit services are operating in New York City. He also commented on the death toll, saying, "I don't think we want to speculate about that -- more than any of us can bear."

  • 3:55 p.m.: White House spokesperson Karen Hughes said the president is at an undisclosed location and is conducting a National Security Council meeting via phone. Vice President Dick Cheney and National Security Advisor Condoleezza Rice are coordinating administration activity in the secure situation room at the White House.

  • 4:00 p.m.: CNN reports that U.S. officials say there are "good indications" that Osama bin Laden is involved in the attacked based on "new and specific" information uncovered since the attacks.

  • 4:25 p.m.: The New York Stock Exchange, American Stock Exchange and the Nasdaq Stock Market announce they will be closed Wednesday.

  • 5:20 p.m.: Building 7 of the World Trade Center development collapses. The 47-story building was damaged in the explosions after the morning plane crashes.

  • 6:00 p.m.: Explosions occur in Kabul, Afghanistan, the likely location of bin Laden. Officials later indicate the U.S. had no involvement in the explosions, likely the result of ongoing civil unrest in the country.

  • 6:54 p.m.: President Bush returns to the White House. It is revealed that Air Force One returned to Washington from Omaha with an escort of three jet fighters.

  • 7:50 p.m.: New York police officials say at least 78 police officers are missing. Fire officials estimates as many as 200 firefighters -- of the 400 first arriving at the World Trade Center -- are likely dead.

  • 8:30 p.m.: In an Oval Office address to the nation, President Bush asks for prayers for those involved in the tragedy. He remains firm, stating, "These acts shatter steel, but they cannot dent the steel of American resolve." Bush indicated the U.S. government would respond appropriately and would make no distinction between the terrorists and those who harbor them.