World Trade Center crumbles in terrorist attack

(CNN) -- Two airplanes crashed separately into the twin towers of the World Trade Center in Lower Manhattan shortly before and after 9 a.m. EDT in terrorist attacks that erased the 110-story towers from the Manhattan skyline.

The FBI was investigating reports that the first plane, a commercial flight from Boston, Massachusetts, may have been hijacked, The Associated Press reported. An eyewitness told CNN that about 8:35 a.m. he saw a 767 flying low down the center of Manhattan and veer left to fly directly into the south side of the north tower.

As witnesses gathered on the street observing the disaster in the north tower, a second, smaller plane crashed into the south tower. The towers can accommodate as many as 50,000 occupants, and witnesses reported that people panicked as smoke and fire swept through the structures.

" People were jumping out of the windows," an unidentified woman said through tears to a CNN reporter. "You can see them jumping out of the windows, if you go by there you can see them jumping out the windows right now!"

The Federal Aviation Administration closed all airports in the United States just before 10 a.m. EDT and routed all international flights bound for New York to Canada.

It was the second terrorist attack at the World Trade Center. Six people died in a basement-level explosion at the towers in February 1993.

New York Mayor Rudy Guiliani said the casualties from the tragedy would be enormous, given the number of business and workers in the towers near the city's financial district.

Hospital emergency rooms throughout the city began receiving hundreds of people suffering from smoke inhalation and critical injuries, CNN's Maria Hinjohosa reported. Passersby by began streaming into the hospitals to donate blood.

Each tower's collapse occurred within 30 minutes of the other, with the south tower crumbling first.

Inches of ash from their destruction cloaked buildings, emergency vehicles and people who were in the immediate area of the disaster. People scrambling from the streets near the building crouched behind cars and covered their heads as police officers screamed for people to leave the area as the south tower began crumbling.