NEW YORK -- A massive explosion Friday ripped through a parking garage underneath the twin towers of the World Trade Center -- New York's tallest buildings -- killing at least seven people, injuring more than 500, sparking fires and collapsing the ceiling of a subway station.
City and federal law enforcement authorities were investigating the possibility that the blast was caused by a powerful bomb placed in the parking garage.
'We have not determined the origin of this explosion,' Police Commissioner Raymond Kelly said.
When asked if it was a bomb, he said, 'That has not been determined. We're still not able to get into the building to get into the origin of the explosion.'
Kelly said police received seven phone calls after the explosion in which the callers claimed responsibility, but he refused to elaborate.
Officials with the Emergency Medical Services said seven people were killed and more than 500 were taken to various Manhattan hospitals with variety of injuries. One firefighter was hurt searching for trapped bodies.
Thick black smoke forced the evacuation of thousands of workers, who streamed out exits under falling snow, sucking fresh air, their faces smeared with soot.Some walked down 100 flights of stairs after elevator service was cut.
The blast shook buildings throughout lower Manhattan, and knocked out plate-glass windows on the ground floor of the two 110-story towers of World Trade Center, the second largest buildigs in the world, where some 50,000 people go to work each day.
Four hours after the explosion, a bomb threat was made against the Empire State Building, which was evacuated by police as a precaution, and at 26 Federal Plaza, the downtown building housing the New York headquarters of the FBI and other federal agencies.
The blast occurred at about 12:18 p.m. on the second of six parking garage levels, pulling down the garage level above it and starting fires in at least two other areas that burned vehicles and electrical equipment.
As many as 30 were hurt by falling debris from a ceiling collapse in a Port Authority Trans Hudson, or PATH, station. PATH trains travel from Manhattan to New Jersey.
Many of New York's commodity markets closed early because of smoke conditions on the trading floor.
