US under terrorist attack: explosions at World Trade Centre, Pentagon on fire, hundreds feared dead

Two planes crashed into the upper floors of both World Trade Center towers minutes apart today, causing one of the buildings to collapse, in what the President George W. Bush said was an apparent terrorist attack, blasting fiery, gaping holes in the 110-storey buildings.

Hundreds are feared dead, with thousands injured, although early reports only confirmed six deaths.

Within the hour, an aircraft crashed on a helicopter landing pad near the Pentagon, and the West Wing of the White House was evacuated amid threats of terrorism, soon after a second explosion was heard at the Pentagon.

The president ordered a full-scale investigation to "hunt down the folks who committed this act."

One of the planes that crashed into the World Trade centre had been hijacked after takeoff from Boston, a U.S. official said, citing a transmission from the plane.

All planes were grounded across the country by the Federal Aviation Administration. All bridges and tunnels into Manhattan were closed down.The twin disaster at the World Trade centre happened shortly before 9 a.m. (1300 GMT) and then right around 9 a.m.

Heavy black smoke billowed into the sky above the gaping holes in the side of the 110-story twin towers, one of New York City's most famous landmarks, and debris rained down upon the street, one of the city's busiest work areas. When the second plane hit, a fireball of flame and smoke erupted, leaving a huge hole in the glass and steel tower.

People ran down the stairs in panic and fled the building. Thousands of pieces of what appeared to be office paper came drifting over Brooklyn, about three miles away.

"Today we've had a national tragedy," Bush said in Sarasota, Fla. "Two airplanes have crashed into the World Trade centre in an apparent terrorist attack on our country." He sairy 1993, killing six people and injuring more than 1,000 others.

Several subway lines were immediately shut down Tuesday. Trading on Wall Street was suspended.

"The plane was coming in low and ... it looked like it hit at a slight angle," said Sean Murtagh, a CNN vice president, the network reported.

"I was watching TV and heard a sonic boom," Jeanne Yurman told CNN. "The side of the World Trade centre exploded. Debris is falling like leaflets. I hear ambulances. The northern tower seems to be on fire."

A senior government official, speaking on condition of anonymity, said the agency is pursuing reports that one or both of the planes were hijacked and that the crashes may have been the result of a suicide mission.

"It certainly doesn't look like an accident," said a second government official, also speaking on condition of anonymity.

In 1945, an Army Air Corps B-25, a twin-engine bomber, crashed into the 79th floor of the Empire State Building in dense fog.

In Florida, Bush was reading to children in a classroom at 9:05 a.m. when his chief of staff, Andrew Card, whispered into his ear. The president briefly turned somber before he resumed reading. He addressed the tragedy about a half-hour later.