NEW YORK, Sept. 11 - Two aircraft slammed into the twin towers of the World Trade Center on Tuesday, causing one to collapse, while another aircraft hit part of the Pentagon. The Pentagon, the West Wing of the White House and the Capitol building were being evacuated. In addition, the FAA grounded all civilian aircraft nationwide. President Bush called the tragedies "an apparent terrorist attack on our country."
NBC'S JIM MIKLASEWSKI, reporting from the Pentagon, said eyewitnesses saw a third aircraft crash into part of the Pentagon.
In New York, the aircraft struck minutes apart, starting fires and sending smoke billowing out of the skyscrapers. The top of the south tower later collapsed onto the street below.
The first crash happened shortly before 9 a.m. ET.
MSNBC.com reporter Martin Wolk, who was inside one of the towers, said the lights flickered and then a loud bang was heard. People panicked and started to flee the building.
When they reached the lobby, smoke started to fill the building and people could see debris falling and many cars outside were damaged. "It was sheer pandemonium, people were screaming and crying, afraid to go outside because of the falling debris," Wolk said. "We looked up and it looked like the top 20 floors were in flames."
Another bystander described a barrage of debris raining down on the sidewalk below
Shortly after 9 a.m., a second aircraft was seen crashing into the other tower. Broadcast cameras already watching the scene filmed the second plane as it slammed into the tower and exploded in a huge fireball.
A half hour later, President Bush made a brief statement to reporters, calling the disaster a "national tragedy" and attributing it to terrorists. He did not cite any specific terrorist groups but vowed to "hunt down the folks who committed this act."
American Airlines later acknowledged that one of its flights had been hijacked Tuesday morning shortly after leaving Boston en route to Los Angeles.
In the wake of the crashes, New York airports and the Lincoln Tunnel were closed as precautionary measures. The stock exchanges in New York also did not open.
Large holes were visible in sides of the 110-story buildings. The tops of the twin towers were obscured by the smoke.
Thousands of pieces of what appeared to be office paper came drifting over Brooklyn, about three miles from the tower, one witness said.
In an earlier terrorist attack, the center was bombed on Feb. 26, 1993, killing six people and injured more than 1,000 others. Terrorist Ramzi Yousef and three others were convicted of orchestrating the attack. Three other indicted co-conspirators remain at large.
Traffic entering New York City from New Jersey was at a standstill approaching the Holland Tunnel as motorists stood outside their cars watching the fire.
In Chicago, the Sears Trade tower was being evacuated as well.
This is a breaking story and will be updated.
The Associated Press contributed to this report.