New York police and fire officials were responding to reports of a massive explosion in Manhattan’s East Harlem, authorities said Wednesday. There were at least 11 minor injuries as clouds of dark smoke rose over the residential neighborhood of red-brick tenements, fire officials said. Metro North commuter rail service, which runs along the site of the blast on Park Avenue, was suspended, officials said. “Two buildings have collapsed. I hope there is no one in there. It’s just rubble,” a worker at a nearby flea market said. Clouds of dark smoke could be seen for a three-block radius as hundreds of rescue officials descended on the scene.