Officials in New York and Washington promptly ruled out terrorism. One person died of cardiac arrest and about 20 others were injured, some seriously, Mayor Michael Bloomberg said at a news conference.
Boiling, brownish water and steam gushed geyser-like at least 120 feet high (36 metres) out of a crater about 20 feet (6 metres) wide on Lexington Avenue at 41st Street, one of the busiest areas of New York City near the Grand Central transportation hub.
The scene evoked memories of buildings collapsing in a billow of debris as they did on Sept. 11, 2001, when the World Trade Center in lower Manhattan was destroyed.
"We ran down 43 floors thinking we were going to die," said Megan Fletcher, 35, who works for an Australian company in the Chrysler Building. "It looked like when the buildings collapsed on 9/11."
Rescue workers and others covered in soot and mud were being decontaminated at the scene by hazardous materials specialists. "The big fear that we have is there may or may not have been asbestos released," Bloomberg said.
The pipe of 24 inches (60 cm) in diameter was installed under Lexington Avenue in 1924, and it carried steam for a variety of industrial purposes, power utility Consolidated Edison
It was the latest public embarrassment for ConEd, which is under scrutiny for power blackouts.
HAVOC AT RUSH HOUR
Pedestrians sprinted from the scene, many with cell phones stuck to their ears, some crying. Some were covered in white ash and soot, others in mud. A badly damaged yellow school bus was stalled in the middle of the street.
"It looked like the World Trade Center had exploded. I saw rocks and pebbles coming down. As I was running I got pelted in the head by rocks and concrete. Steam came up and then the ground started breaking up," said Reggie Evans, an office administrator who was covered in mud.
The geyser was contained about 90 minutes after the pipe exploded, revealing a truck stuck in the crater. Six square blocks were cordoned off, and subway service on Manhattan's crowded East Side was disrupted.
"There was steam and mud coming up to the 12th floor," said Doron Sher, 29, a real estate broker who works on the 12th floor of a building next to the explosion. "We thought it's like a bomb or hurricane."
The blast created havoc at rush hour. Nearly 200 firefighters rushed to the scene, which was crowded with ambulances and fire engines. People wore masks to avoid breathing pollutants.
Kwang Choi, 57, was working at a laundromat one block away when the explosion occurred. "People just kept running. People were saying a building collapsed," he said. "I looked outside -- huge smoke, just like 9/11. I just ran."
Said 50-year-old computer worker Azad Mohamed: "Of course, the first thing you think about is terrorism. It's pretty scary."
