New York Mayor Bill de Blasio told reporters at the scene that there are a "number of missing individuals" and every effort would be made to verify their safety and whereabouts.
"From what we know now, the only indication of danger came 15 minutes earlier when a gas leak was reported to ConEd," the mayor said. "The explosion happened before that team arrived."
"This is a tragedy of the worst kind, because there was no indication in time to save people," de Blasio said.
Smoke billowed into Central Park and could be seen from miles away in midtown, and New Yorkers said they felt rumbles as far away as 150th Street. Closer to the collapse, groceries were knocked from store shelves and debris floated through the air.