A massive fire broke out after an explosion in a building in New York City's East Village neighbourhood, leaving 12 injured, three critically, the Mayor Bill de Blasio said.The explosion on Thursday afternoon caused partial collapse of the building and more than 200 firefighters responded to the ensuing blaze engulfing the five-story commercial and residential building in Manhattan, a FDNY spokesperson has said, Xinhua reported.Heavy smoke billowed from the building near Second Avenue and Seventh Street. Flames also spread to nearby buildings.Andrew, who was in an apartment across the street when the explosion took place around 15.20 pm, said, "The building shook. We thought something happened on the roof, and then we came outside. There was a bunch of people running around screaming.""At one point we can see the flame above the building, over the horizon of the other buildings. It was really scary. At that point, they started to clear us out of that block," he added.Mayor de Blasio said at a press conference on site that the explosion affected four buildings, and two of them collapsed.Preliminary evidence suggested a gas-related explosion, and investigation is still ongoing. The initial impact appears to have been caused by plumping and gas work inside one building, he added.The area was being evacuated, and other people were being evaluated at the scene.Con Edison, New York's electric and natural gas services provider, said it has shut down gas service in the area.