An explosion ripped through a midtown Manhattan street during the evening rush hour yesterday, sending steam belching out of a gaping hole in the ground.

Police said that the incident did not appear to be terrorism-related.

One person died of a heart attack and another was critically injured in the blast from an underground steam pipe at East 41st Street and Lexington Avenue. At least 15 others suffering from burns and minor injuries.

Andrew Troisi, of New York’s Office of Emergency Management, said: “It was a 20in steam main that appears to have exploded. There is no indication of any criminality.”

The fire brigade declared a major emergency and cordoned off streets as plumes of thick grey smoke billowed from the 30ft hole in the ground, spewing a dirty brown sludge like a geyser. Strewn around the hole was the debris of broken concrete and tarmac.

The incident happened at around 6pm in the streets neighbouring Grand Central station, one of the main arterial rail and subway stations in Manhattan. Lines on the subway were shut down last night.

After the initial explosion, smoke rose as high as the 30th floors of the office buildings that run along Lexington Avenue, within site of the art deco Chrysler Building.

Next to the huge hole in the ground was a yellow school bus, with its doors wide open and lights flashing. One policeman on the scene said that the bus had been yards away at the time of the explosion but was able to stop just in time.

“We have a building that’s a bit shaky but nothing has collapsed,” a police spokeswoman said, contradicting a witness report from the scene that a building had collapsed.

One bystander said that she had been asked to evacuate her office building on Lexington Avenue but that, as she left, concrete and glass began to fall on to the pavement. No one was bloodied but plenty were spattered with brown sludge from the explosion.

An investment banker who was in a nearby building said that people feared that the explosion, which came a day after a US intelligence report suggested that Islamic extremists were intent on attacking the United States, was a terror attack. “We heard this vast explosion. The building shook a bit and small particles of rock came to our window on the 27th floor,” he told local television.

“We decided to get the hell out of there. We took the elevator downstairs. There were a lot of people on it. I dashed out with the rocks falling on me. Obviously everybody thinks of 9/11 — a repeat. It was a very powerful explosion, the most powerful explosion I have ever been close to. It was like a volcano.”

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