8:45 a.m. ET A hijacked American Airlines commercial jetliner - Flight 11, which left Boston en route to Los Angeles with 92 people aboard - slams into the 110-story north tower of the World Trade Center in lower Manhattan.

9:03 a.m. A second hijacked plane - United Airlines Flight 175, which was seized while carrying 65 people from Boston to Los Angeles - screeches across the New York sky and explodes into the side of the second World Trade Center tower.

9:31 a.m. President Bush, in Sarasota, Fla., calls the crashes "an apparent terrorist attack." He also says he will order "a full-scale investigation to hunt down and to find those folks who committed this act. Terrorism against our nation will not stand."

9:43 a.m. Another hijacked commercial jetliner, American Airlines Flight 77 carrying 64 people, crashes into the Pentagon in Washington, collapsing part of one of the building's five sides.

After 9:30 a.m. U.S. government buildings in Washington, including the Capitol and the White House, are evacuated with officials citing a credible threat of a terrorist attack. More buildings are evacuated and shut down throughout the day.

9:49 a.m. The Federal Aviation Admini- stration shuts down all aircraft takeoffs nationwide and orders planes already in the air to land at the closest airport. Canadian airports begin letting U.S. flights land in Canada.

9:50 a.m. Two World Trade Center tower - the second building hit in New York - collapses, about an hour after being hit by the plane. Casualties are reported extremely high - possibly in the thousands - but figures are not known.

10:10 a.m. A fourth hijacked jetliner - United Flight 93 from Newark, N.J., headed for San Francisco with 45 people - crashes in western Pennsylvania, about 80 miles southeast of Pittsburgh.

10:28 a.m. The second tower - One World Trade Center - collapses in New York. The city's famed skyline is forever altered.

About 10:30 a.m. All U.S. financial markets suspend trading in the wake of the attacks. The New York Stock Exchange had closed already at 9:40 a.m.

10:38 a.m. A fourth explosion rocks the collapsed remains of the World Trade Center. Broken gas lines are suspected.

About 11 a.m. New York City Mayor Rudy Giuliani calls for evacuation of lower Manhattan. All federal government facilities in the nation's capital and New York City are officially closed.

1:20 p.m. President Bush leaves Barksdale Air Force Base, La., for a secure, undisclosed location.

5:25 p.m. Eight hours after the morning crashes, fire was raging at adjoining 7 World Trade Center, eventually causing its collapse. The evacuated building was damaged when the tower above it collapsed.

7:20 p.m. President Bush declares New York a major disaster in the wake of the attacks on the World Trade Center.