Attack on the World Trade Center | Attack on the Pentagon
Anatomy of terrorist attacks | How the buildings most likely collapsed

Establishing the U.S. death toll could take weeks. The four airliners alone had 266 people aboard, and there were no known survivors. At the World Trade Center, an estimated 300 firefighters may have died, and as many as 80 police officers are believed to be missing.

A timeline of the attacks in the United States on Tuesday (times EDT), according to witnesses, authorities and media reports:

7:59 a.m. - American Airlines Flight 11, carrying 92 people, leaves Boston's Logan International Airport for Los Angeles, according to Massachusetts Port Authority.

8:01 a.m. - United Airlines Flight 93, carrying 45 people, leaves Newark, N.J., International Airport for San Francisco, according to airline.

8:14 a.m. - United Airlines Flight 175, carrying 65 people, leaves Boston for Los Angeles, according to port authority.

8:45 a.m. - American Flight 11 crashes into north tower of World Trade Center.

9:03 a.m. - United Flight 175 crashes into south tower of World Trade Center.

9:31 a.m. - In Florida, President Bush calls the crashes an "apparent terrorist attack on our country."

9:40 a.m. - American Airlines Flight 77, carrying 64 people from Washington to Los Angeles, crashes into Pentagon. Trading on Wall Street called off.

9:48 a.m. - The Capitol and West Wing of the White House are evacuated.

9:49 a.m. - The Federal Aviation Administration bars aircraft takeoffs across the country. International flights in progress told to land in Canada.

9:50 a.m. - Two World Trade Center - the south tower - collapses.

9:58 a.m. - Emergency dispatcher in Pennsylvania receives call from a passenger on United Flight 93, who says: "We are being hijacked, we are being hijacked!"

10 a.m. - United Flight 93 crashes 80 miles southeast of Pittsburgh.

10:29 a.m. - One World Trade Center - the north tower - collapses.

10 a.m.-11:30 a.m. - Government buildings across nation are evacuated, including the Capitol and the White House. The United Nations closed down. The Securities and Exchange Commission closes all U.S. financial markets for the day. New York City Mayor Rudolph Giuliani calls for evacuation of lower Manhattan.

11:40 a.m. - Bush arrives at Barksdale Air Force Base, La., from Florida after deciding not to return to Washington right away. He later travels to U.S. Strategic Command at Offutt Air Force Base, Neb.

2:51 p.m. - The Navy dispatches missile destroyers and other equipment to New York and Washington.

5:25 p.m. - Seven World Trade Center collapses.

7 p.m. - Bush arrives in Washington from Nebraska.

Sources: Skilling Ward Magnusson Barkshire; Port Authority of New York and New Jersey: Knight Ridder Newspapers; New York Times; The Associated Press