NEW YORK (AP) — Emergency workers are painstakingly looking for signs of two missing people in the rubble of three New York City apartment buildings leveled in an apparent gas explosion, though authorities acknowledge the chances of finding them are slim.

Meanwhile, investigators are working to piece together exactly what caused the blast Thursday that injured 22 people in Manhattan's East Village. Consolidated Edison says utility workers discovered in August that the gas line to a restaurant in one of the buildings had been tapped, creating a "hazardous situation." The workers found multiple leaks in the line that were later repaired.

City officials suspect leaking natural gas was the source of the explosion, which sparked a raging blaze that took hundreds of firefighters to quell.

Officials estimate it could take a week of 24-hour-a-day work to sift through the heap of loose brick, wood and debris.

(Story by: Jennifer Peltz, The Associated Press)