SURFSIDE, Florida — Demolition crews set off explosives late Sunday to bring down the damaged remaining portion of a collapsed South Florida condo building, a key step to resuming the search for victims as rescuers possibly gain access to new areas of the rubble.

A loud rat-at-tat of explosions echoed from the structure just before 10:30 p.m. Then the building began to fall, one floor after another, cascading into an explosion of dust. Plumes billowed into the air, as crowds watched the scene from afar.