Suffolk County police say surrounding houses also were damaged during the blast Tuesday in Brentwood.
The injured include a toddler, a plumber and several rescuers. Their conditions are not known.
A fire official says propane was being investigated as a possible cause.
Neighbors many blocks away reported feeling their own homes shake.
Dave Grant heard the explosion and raced about seven blocks to the scene. He heard one officer yelling “We need help!” He assisted other officers as they lifted the collapsing roof to rescue a man.
WCBS Radio says a neighbor’s arms and hands were bloodied from digging through the rubble.