The Pentagon took a direct, devastating hit from an aircraft and the enduring symbols of American power were evacuated Tuesday as an apparent terrorist attack quickly spread fear and chaos in the nation's capital.
The nerve center of the nation's military burst into flames and a portion of one side of the five-sided structure collapsed when the plane struck in midmorning. Secondary explosions were reported in the aftermath of the attack and great billows of smoke drifted skyward toward the Potomac River and the city beyond.
Authorities immediately began deploying troops, including a regiment of light infantry.
"Terrorism against our nation will not stand," vowed President Bush, in Florida on a morning when not only Washington was struck, but the twin towers of the World Trade Center in New York were hit by planes and later collapsed.
There was no attempt to minimize the impact.
"This is the second Pearl Harbor. I don't think that I overstate it," said Sen. Chuck Hagel, R-Neb., referring to the attack 60 years ago that surprised the nation and propelled it into World War II.
With Bush in Florida, his advisers were preparing a list of options, including closing the nation's borders, according to a senior U.S. official.
The source, who spoke on condition of anonymity, said it was premature to discuss military options because investigators were still trying to determine who was responsible for the attacks.
Away from the Pentagon, unexplained explosions were reported in the vicinity of the State Department and the Capitol. Agents with automatic weapons patrolled the White House grounds.
The departments of Justice, State, Treasury and Defense and the Central Intelligence Agency were evacuated -- an estimated 20,000 at the Pentagon alone.
One lawmaker said the congressional leadership had been hustled away to safety.
And the FAA ordered the entire nationwide air traffic system shut down.
A torrent of people rushed from their office buildings throughout the nation's capital, eager to leave a city under siege. The cell phone networks were overloaded, clusters of people sprayed on the sidewalks and at least one suburban school district announced plans to close early.
The Pentagon was hit a short while after the World Trade Center was struck.
Paul Begala, a Democratic consultant, said he witnessed an explosion near the Pentagon, saying it sent a huge, orange fireball skyward.
AP reporter Dave Winslow also saw the crash. He said, "I saw the tail of a large airliner. ... It plowed right into the Pentagon."
Gen. Richard Myers, vice chairman of the Joint Chiefs of Staff, said that prior to the crash into the Pentagon, military officials had been notified that another hijacked plane had been heading from the New York area to Washington. He said he assumed that hijacked plane was the one that hit the Pentagon, though he couldn't be sure.
One of two planes that crashed into the World Trade Center was hijacked after takeoff from Boston and headed to Los Angeles with 92 aboard, American Airlines disclosed.
The second plane may have flown out of Newark, N.J., the official said, speaking on condition of anonymity.
Asked if there was any possibility the crashes were anything other than deliberate, a government official said it appeared not to be an accident.