NEW YORK – When the skyscraper-sized geyser of steam and debris cleared, it left a gaping crater, hobbled subways and shattered windows in the heart of midtown Manhattan. It also left one woman dead and countless people worried about their air quality.

Crews worked overnight to assess and repair the damage after a steam pipe exploded Wednesday underneath a street near Grand Central Terminal, sending people running for cover as debris rained down. About 30 people were injured, at least four seriously, officials said.

For some witnesses, the explosion, dust, debris and chaos were frighteningly reminiscent of the scene on Sept. 11, 2001. But officials quickly ruled out terrorism and said the explosion was caused by the rupture of the 83-year-old steam pipe.

“We were scared to death. It sounded like a bomb hit or a bomb went off, just like 9/11. People were hysterical, crying, running down the street,” said Karyn Easton, a customer at a salon a few blocks from the site of the blast. “It was really surreal.”

Environmental officials were testing for air contamination, fearing that the ruptured pipe may have been wrapped in asbestos, a carcinogen that can cause fatal lung disease, though disease is often linked to prolonged exposure.

“The big fear that we have is there may or may not have been asbestos release,” Bloomberg said. But he said that if the chemical had been released, it might have washed away with the water that came with the steam.

The city told people in nearby buildings to keep windows closed and air conditioners set to recirculate indoor air instead of drawing it from outside, and anyone exposed to the falling debris was instructed to wash carefully and isolate soiled clothing in plastic bags.

City engineers warned that up to six feet surrounding the giant hole might be in danger of further collapse. Stretches of several major thoroughfares remained closed early Thursday, and city officials said workers would not be allowed into office buildings in a zone that covered several blocks.

Steam and dirt boiled from the ground for hours after the initial eruption, generating a tremendous roar and spraying vapor as high as the top of the nearby Chrysler Building. The 200-degree steam was under 150 pounds of pressure per square inch when it exploded near East 41st Street and Lexington Avenue.

Many people were struck by falling chunks of asphalt or rock that had been blasted out of the ground. Mud covered some bystanders. A woman who was bleeding profusely was helped by police while a man lay on a stretcher in the street.

When the steam dispersed almost two hours after the explosion, a crater many feet wide was visible in the street. A red truck lay at the bottom of the hole. Two city buses and a small school bus sat abandoned in the middle of Lexington Avenue, covered with grit.

Authorities couldn’t immediately account for how the most seriously wounded victims were hurt. Police said the woman who was killed, identified as Lois Baumerich, 57, of Hawthorne, N.J., died of cardiac arrest.

She and 15 other people were taken to Bellevue Hospital, said hospital spokesman Stephen Bohlen. Two seriously injured patients were being treated in the hospital’s trauma unit. The remainder suffered minor injuries, he said.

Two people were in critical condition at New York Weill-Cornell Medical Center, said hospital spokeswoman Emily Berlanstein.

Among the injured were several firefighters and police Officer Robert Mirfield, who helped evacuate 75 people trapped in a nearby office building by cutting open a gate, authorities said.

The cause of the rupture remained under investigation. Officials said the pipe, installed in 1924, might have exploded under extreme pressure caused by an infiltration of cold rainwater, or might have been damaged by a water main break.

Con Edison head Kevin Burke said the site of the explosion had been inspected hours before the blast, as part of a routine response to heavy rains that flooded parts of the city. He said crews had found nothing as they searched for steam rising from manhole covers or cracks in the street _ indications that pipes could be in jeopardy. The steam systems are normally inspected about every six weeks.

The Buildings Department determined late Wednesday that nearby buildings were structurally sound but suffered some water damage and broken windows.

Millions of pounds of steam are pumped beneath New York City streets every hour, heating and cooling thousands of buildings, including the Empire State Building.

The steam pipes have proven prone to rupture before. A steam pipe explosion near Gramercy Park in 1989 killed three people and spewed loads of asbestos into the air _ a fact that Con Ed later admitted it concealed for days while residents were exposed.

That explosion was caused by a condition known as “water hammer,” in which water condenses in a closed section of pipe. The sudden mix of hot steam and cool water can cause pressure to skyrocket, bursting the pipe.

Associated Press Writers Eric Vora, Richard Pyle, Tom Kent, Tom Hays, Marcus Franklin, David B. Caruso and Verena Dobnik and AP National Writer Deborah Hastings contributed to this report.

A service of the Associated Press(AP)