New York, Sept. 11 (Bloomberg) -- Terrorists hijacked commercial airliners and crashed them into the World Trade Center and the Pentagon in the biggest terrorist attack in U.S. history.
The crashes and subsequent explosions destroyed the twin towers, a 110-story office complex on Manhattan's southern tip, through which as many as 200,000 people pass every weekday. The number of deaths couldn't be determined.
President George W. Bush vowed to ``hunt down and find those folks who committed this attack.'' No group claimed responsibility.
A plane with about 300 people on board also crashed outside Pittsburgh. A plane attempting a second attack on the Pentagon was forced down near Camp David, the presidential retreat in Maryland.
Authorities ordered all U.S. airports shut down, and air travel around the world was disrupted. The bridges and tunnels leading out of New York City were closed, and New York's mayoral primary election was canceled. The Sears Tower in Chicago was evacuated, and the Securities and Exchange Commission ordered U.S financial markets closed.
Blasts rocked the trade center about 9 a.m. New York time after the planes crashed into the building. Workers leaped to their deaths as flames and smoke poured from the upper floors. One tower collapsed at 10 a.m. and the other fell at 10:28 a.m. as police and fire officials scrambled to clear the area.
``We heard an explosion,'' said Mark Heyman, a tourist from Burlington, Vermont, who was in one of the towers when the plane hit. ``We felt a huge crash and the building shook. We saw debris coming down and we ran.''
A United Airlines plane was hijacked, a worker for the airline told Cable News Network. The FBI was investigating a hijacking before the crashes, CNBC reported. In addition, an American Airlines Boeing 767 that departed from Boston was one of the airplanes that crashed into the building.
`Can't Believe It'
Shoes, personal clothing, luggage were scattered for blocks, around the towers, along with pieces of airplane and broken glass everywhere. Police official said they evacuated a six-block area.
``I've seen seven people jump,'' said Elizabeth Dziejma, a maintenance worker at Merrill Lynch & Co. who was evacuated from one of the towers. ``Jesus Christ, this is awful. I can't believe it.''
Witnesses who heard the initial plane crash witnessed the second attack.
Ijust went outside to see what was going on,'' said Gary Braitman, a consultant who lives in Greenwich Village. ``Then I saw this jet plane flying. I thought, it's really low, that's weird. It banked. It went right into the building. ... That is one of the scariest things I've seen in my life.''
From 150,000 to 200,000 people pass through the complex on a typical weekday, including 40,0000 who work there and 50,000 commuters who take trains that connect New York and New Jersey and terminate at the towers.
``Injured are coming through the emergency room doors constantly; I'm certain it's in the hundreds,'' said Kathleen Zichy, a senior vice president at NYU Downtown Hospital, which is just blocks from the World Trade Center. ``I have never seen anything the equal of this, in 10 years'' at the hospital, Zichy said, coughing from the dust that has spread through the financial district after the collapse.
Lehman Brothers Holdings Inc., located in the adjacent World Financial Center, closed its trading operations. Merrill Lynch and other firms didn't answer their telephones.
The attack was the second on the World Trade Center. In February 1993 terrorists set off a bomb in an underground garage at a spot they believed would cause the collapse of both towers. That explosion killed six. Ramzi Yousef was convicted of masterminding the bombing.
The twin towers, a 10-million square foot complex, are owned by the Port Authority of New York and New Jersey. Morgan Stanley Dean Witter & Co. is the largest tenant in the complex, which is also home to offices of Credit Suisse First Boston, Bank of America and Deutsche Bank.
The Federal Aviation Administration ordered all U.S. planes grounded and the U.S. Capitol and other federal buildings including the Treasury Dept. were evacuated.
A commercial airliner crashed in Somerset County, Pennsylvania, said Maria Smith, a spokeswoman for the Pennsylvania Emergency Management Agency. The crash occurred 70 miles southeast of Pittsburgh.
There were about 300 people on board, she said. Authorities don't know where the plane took off, where it was headed or the nationalities of the passengers, Smith said.