We do move on and to those stunning images from that massive inferno, tear plug a luxury apartment building. More than 1,000 people homeless this evening a state of emergency declared for a time. Just across the river in new Jersey, that iconic New York skyline in the distance. The devastation from above, plumes of black smoke there. Chunks of the building simply melting away. Tonight, officials saying so many lives were saved because that fire broke out when many were not yet home. Now, revealing something else about how the fire started. ABC's Tom llamas on the scene. Reporter: Tonight, more than 1,000 people in New Jersey left homeless. Last night, this massive fire, the size of an entire city block, wiped out a luxury apartment complex. Just listen to the roaring flames. And watch closely. This eyewitness video shows a firefighter lifting aesident out from the inferno. I have nothing. I feel so bad for all those families. Reporter: The fire sky high, seen for miles, and across the Hudson in Manhattan. New York City's fire department even crossing state lines to lp out. In total, 500 first responders from both states called into action. Firefighters say the biggest challenge? The structure's lightweight construction. The fire feeding on the wooden skeleton and the truss style roof. Up to New Jersey code but cheaper to build. If it was made out of concrete and cinder block, we wouldn't have this problem. Reporter: When you look down at all that destruction, it's hard to believe, but everyone got out alive. In fact, there was only minor injuries. And tonight, we know how this fire started. Fire officials say the maintenance staff working on some plumbing somehow ignited the blaze. They're calling this an accident. A big accident. David? Tom llamas tonight. Tom, thank you.