8:30 p.m. (all times are EDT): President Bush addresses the nation, saying "thousands of lives were suddenly ended by evil" and asks for prayers for the families and friends of Tuesday's 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 harbor them. He adds that government offices in Washington are reopening for essential personnel Tuesday night and for all workers Wednesday.

WTC devastation

7:45 p.m.: 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 were killed.

7:02 p.m.: CNN's Paula Zahn reports the Marriott Hotel near the World Trade Center is on the verge of collapse and says some New York bridges are now open to outbound traffic.

7:17 p.m.: U.S. Attorney General John Ashcroft says the FBI is setting up a Web site for tips on the attacks: www.ifccfbi.gov. He also says family and friends of possible victims can leave contact information at 800-331-0075.

6:54 p.m.: Bush arrives back at the White House aboard Marine One and is scheduled to address the nation at

8:30 p.m. The president earlier landed at Andrews Air Force Base with a three-fighter jet escort. CNN's John King reports Laura Bush arrived earlier by motorcade from a "secure location."

Stunned onlookers

6:40 p.m.: U.S. Defense Secretary Donald Rumsfeld holds a news conference in the Pentagon, noting the building is operational. "It will be in business tomorrow," he says.

6:10 p.m.: Mayor Rudolph Giuliani urges New Yorkers to stay home Wednesday if they can.

6 p.m.: Explosions are heard in Kabul, Afghanistan, hours after terrorist attacks targeted financial and military centers in the United States. The attacks occurred at 2:30 a.m. local time. Afghanistan is believed to be the home of Saudi militant Osama bin Laden, who U.S. officials say is possibly behind Tuesday's deadly attacks. U.S. officials say later that the United States had no involvement in the incident whatsoever.

5:30 p.m.: CNN Senior White House Correspondent John King reports that 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 U.S. Capitol building.

5:20 p.m.: The 47-story Building 7 of the World Trade Center complex collapses. The evacuated building is damaged when the twin towers across the street collapse earlier in the day. Other nearby buildings in the area remain ablaze.

Soot-covered man

5:15 p.m.: CNN Military Affairs Correspondent Jamie McIntyre reports fires are still burning in part of the Pentagon. No death figures have been released yet.

4:30 p.m.: The president leaves Offutt Air Force Base in Nebraska aboard Air Force One to return to Washington.

4:25 p.m.: The American Stock Exchange, the Nasdaq and the New York Stock Exchange say they will remain closed Wednesday.

New York Mayor Giuliani

4:20 p.m.: U.S. Sen. Bob Graham, D-Florida, chairman of the Senate Intelligence Committee, says he was "not surprised there was an attack (but) was surprised at the specificity." He says he was "shocked at what actually happened -- the extent of it."

4:10 p.m.: Building 7 of the World Trade Center complex is reported on fire.

4:06 p.m.: California Gov. Gray Davis dispatches urban search-and-rescue teams to New York City.

4 p.m: CNN National Security Correspondent David Ensor reports that U.S. officials say there are "good indications" that bin Laden is involved in the attacks, based on "new and specific" information developed since the attacks.

3:55 p.m.: Giuliani now says the number of critically injured in New York City is up to 200 with 2,100 total injuries reported.

3:55 p.m.: Karen Hughes, a White House counselor, says the president is at an undisclosed location, later revealed to be an 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. Defense Secretary Donald Rumsfeld is at the Pentagon.

2:49 p.m.: 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."

2:30 p.m.: The FAA announces there will be no U.S. commercial air traffic until noon EDT Wednesday.

"Attacks cowardly"

2 p.m.: Senior FBI sources tell CNN they are working on the assumption that the four airplanes that crashed were hijacked as part of a terrorist attack.

1:48 p.m.: President Bush leaves Barksdale Air Force Base in Louisiana aboard Air Force One and flies to an undisclosed location.

1:44 p.m.: The Pentagon says five warships and two aircraft carriers will 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, are headed for the New York coast. The other ships headed to sea are frigates and guided missile destroyers capable of shooting down aircraft.

1:27 p.m.: A state of emergency is declared by the city of Washington.

1:04 p.m.: Bush, speaking from Barksdale Air Force Base, 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."

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.

Second tower falls.

12:15 p.m: San Francisco International Airport is evacuated and shut down. The airport was the destination of United Airlines Flight 93, which crashed in Pennsylvania.

12:04 p.m.: Los Angeles International Airport 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 Washington's Dulles Airport to Los Angeles, had 58 passengers and six crew members aboard. Flight 11 slammed into the north tower of the World Trade Center.

11:16 a.m.: CNN reports that the Centers for Disease Control and Prevention is preparing emergency-response teams in a precautionary move.

11:02 a.m.: Giuliani urges New Yorkers 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.

First tower falls.

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.

Pennsylvania crash scene

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.

Pentagon burns.

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.

9:57 a.m.: Bush departs from Florida.

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.

Plane hits WTC.

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.

9:30 a.m.: 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.