Times are CST
12:30 p.m.: The FAA says 50 flights are in U.S. airspace, but none are reporting any problems.
12:15 p.m.: 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.
12:15 p.m: San Francisco International Airport is evacuated and shut down. The airport was the destination of American Airlines Flight 77, which was one of the aircraft to strike the World Trade Center.
12:04 p.m.: Los Angeles International Airport, the destination of two of the hijacked American Airlines flights, is evacuated.
11:59 a.m.: United Airlines confirms that Flight 175, from Boston to Los Angeles, has crashed with 56 passengers and nine crew members aboard. Emergency personnel at the scene say there are no survivors.
11:26 a.m.: United Airlines reports that United Flight 93, en route from Newark, New Jersey, to San Francisco, has crashed in Pennsylvania, southeast of Pittsburgh. The airline also says that it is "deeply concerned" about United Flight 175.
11:18 a.m.: American Airlines reports it has lost two aircraft. American Flight 11, a Boeing 767 flying from Boston to Los Angeles, had 81 passengers and 11 crew aboard. Flight 77, a Boeing 757 en route from Dulles Airport near Washington to Los Angeles, had 58 passengers and six crew members aboard. Flight 11 is believed to be one of the planes that crashed into the World Trade Center.
11:16 a.m.: CNN reports that the Centers for Disease Control and Prevention is preparing bioterrorism teams to respond to the incidents in a precautionary move. The preparation is not based on any known bioterrorism threat.
11:02 a.m.: New York Mayor Rudy Guiliani urges citizens to stay at home and orders an evacuation of the area south of Canal Street.
10:57 a.m.: New York Gov. George Pataki says all state government offices are closed.
10:54 a.m.: Israel evacuates all diplomatic missions.
10:53 a.m.: New York's primary elections scheduled for today are postponed.
10.48 a.m.: Police confirm the crash of a large plane in Somerset County, Pennsylvania.
10.46 a.m.: U.S. Secretary of State Colin Powell cuts short his trip to Latin America to return to the United States.
10:45 a.m.: All federal office buildings in Washington are evacuated.
10:28 a.m.: The World Trade Center's north tower collapses from the top down as if it were being peeled apart, releasing a tremendous cloud of debris and smoke.
10:24 a.m.: The FAA reports that all inbound transatlantic aircraft flying into the United States are being diverted to Canada.
10:22 a.m.: In Washington, the State and Justice departments are evacuated, along with the World Bank.
10:13 a.m.: The United Nations building evacuates, including 4,700 people from the headquarters building and 7,000 total from UNICEF and U.N. development programs.
10:10 a.m.: United Airlines Flight 93 crashes in Somerset County, Pennsylvania, southeast of Pittsburgh.
10:10 a.m.: A portion of the Pentagon collapses.
10:08 a.m.: Secret Service agents armed with automatic rifles are deployed into Lafayette Park across from the White House.
10:05 a.m.: The south tower of the World Trade Center collapses, plummeting into the streets below. A massive cloud of dust and debris forms and slowly drifts away from the building.
9:45 a.m.: The White House evacuates.
9:43 a.m.: An aircraft crashes into the Pentagon, sending up a huge plume of smoke. Evacuation begins immediately.
9:40 a.m.: The FAA halts all flight operations at U.S. airports, the first time in U.S. history that air traffic nationwide has been halted.
9:39 a.m. President Bush is to convene a national security meeting immediately upon his return to Washington. The president has spoken with Vice President Dick Cheney and New York Gov. George Pataki.
9:30 a.m.: President Bush, speaking in Florida, says the country has suffered an "apparent terrorist attack."
9:21 a.m.: New York City Port Authority orders all bridges and tunnels in the New York City area closed
9:17 a.m.: The FAA shuts down all New York City area airports.
9:03 a.m.: A second plane, apparently a passenger jet, crashes into the second World Trade Center tower and explodes. Both buildings are burning.
8:45 a.m.: A large plane, possibly a hijacked airliner, crashes into one of the World Trade Center towers, tearing a gaping hole in the building and setting it afire.
-- MadHat at unspecific.com