The crash of two aircraft into the towers of the World Trade Center in New York this afternoon appears to be an act of terrorism, a US official said.
"It does appear to be terrorist related," said the official, who asked not to be identified.
Another plane crash has been confirmed near the Pentagon in Washington. The White House and the Pentagon have been evacuated.
One of the planes is reported to be an American Airlines 767 hijacked from Boston.
The official said the assessment was based on the action itself, two successive crashes into the twin towers of the World Trade Center within 18 minutes of each other.
There are some reports the planes involved in the crash were hijacked. Reports have also indicated that a third plane has been hijacked.
The World Trade Center consists of two 110-story skyscrapers and are New York's tallest towers. One of the towers is just six feet (two metres) taller than the other.
About 40,000 people work inside the two-building center; more than 150,000 people enter the complex every day for business and pleasure.
On February 26th, 1993, a terrorist bomb exploded in building number one's lower level.
AFP