An explosion at a shoe store sheared the side off a six-story building today, killing at least 18 people, injuring 82 and leaving up to 15 missing. A gas leak was believed to have caused the blast.

The 8:35 a.m. explosion ripped a 50-foot-wide hole up the side of the building. It left a tangle of concrete and steel beams that filled a city block and shattered windows in buildings and cars.

"There were just parts of bodies lying in the street -- torsos, bones -- cars blasted against the building," said Ramon Camino, a doctor who arrived at the scene shortly after the explosion.

Rescue workers pulled dozens of survivors, coated with blood and dust, from the debris. Bodies, bloody and burned, could be seen in the rubble. President Clinton declared a state of emergency, ordering federal aid to supplement local recovery efforts.

Police Chief Pedro Toledo said a propane gas leak may have been the cause of the blast at the Humberto Vidal shoe store in Rio Piedras, a residential and shopping district in San Juan.

Owners of the shoe store said they reported a gas leak to the San Juan Gas Co. several days ago, he said.

Gas company workers had visited the site Wednesday and returned early today to continue repairs, Toledo said. Fire officials said utility employees were working on a gas main outside the building when the blast occurred.

Two hours after the blast, workers rescued a woman from the store. Her daughter, age unknown, remained trapped but was believed to be alive. CAPTION: Police and rescue workers survey the wreckage of a San Juan shoe store after blast apparently caused by a gas leak. CAPTION: Workers dig through rubble of San Juan shoe store after deadly blast believed to have been caused by leaking gas.(Photo ran in an earlier edition)