An explosion in a steam pipeline in Midtown Manhattan sparked panic among evening rush hour commuters on Wednesday, rekindling memories of the September 11 attacks among jittery New Yorkers. One person died of a cardiac arrest while around 20 civilians were injured, some of them seriously, Mayor Michael Bloomberg told reporters. Three or four firefighters were meanwhile treated for minor injuries at the scene, he said. "There is no reason to believe whatsoever that this is anything other than a failure of our infrastructure," Bloomberg said, dismissing any possibility of a terrorist link in the blast in one of New York`s busiest business districts. He said that a 60-centimeter (24-inch) steam pipe installed in 1924 and used in the heating and cooling systems of office buildings in the area had burst, possibly due to rain water from a morning deluge seeping into the pipe. While police were quick to say there was nothing to indicate the explosion near Grand Central station was terrorist related, for some New Yorkers, the incident immediately rekindled memories of the September 11 attacks of 2001. "Obviously everybody thinks immediately of 9/11," said Heiko Thieme, 63, who was on the 27th floor of a building overlooking the site of the underground explosion at Lexington Avenue and 41st street at the time of the blast. "It was the most awful thing I`ve seen. I`ve seen a lot of things in my life," he told AFP. The explosion, which left a crater in the middle of the street, sent clouds of steam, mud and rocks several stories into the air and left buildings in the area shaking while a lingering rumble could be heard several blocks away. "This was a major explosion. The ground was literally shaking under your feet," NYPD assistant police commissioner Paul Browne told CNN television. Police earlier said the blast may also have involved a transformer exploding. "Everything shook, there was a big explosion," said Lilian Crespo, 33. "It was horrible." "I heard a huge vibration and we were evacuated from the building, everybody was panicking," added another witness, Henry Galarza. Grand Central Terminal, a major subway and commuter rail hub, was shut down while a handful of surrounding buildings were evacuated and subway services severely disrupted. Rail services resumed later in the evening. Several blocks of Lexington Avenue outside Grand Central Terminal near the iconic art deco Chrysler building remained shut off into the evening. The explosion occurred just before 6:00 pm (2200 GMT) and sent crowds of people heading north from the area, many of them running. A spokesman for electrical supplier Con Edison said the company was testing the air for asbestos as a precaution. A similar steam pipe explosion in 1989 killed three people and caused a health alert due to asbestos being released into the air. New York has been on a heightened state of alert ever since the September 11 attacks and any large scale emergency prompts a certain degree of panic among a jittery population. The explosion came just a day after a US intelligence report suggested that Islamic extremists were intent on attacking the United States.