ASUNCION, Paraguay ? At least 256 people were killed after a propane gas tank exploded inside a crowded supermarket here, igniting a fast-moving fire that left a crowd of Sunday shoppers trapped behind doors that may have been locked to prevent looting.

Witnesses said the explosion took place about noon in a basement food-court kitchen where families had gathered for lunch in the modern, mall-sized market.

Officials said many bodies were yet to be recovered and the death toll could surpass 300, making the blaze among the deadliest in recent South American history. Public Health Minister Julio Cesar Velazquez described a gruesome scene at the Ycua Bolanos supermarket and at a temporary morgue set up in the parking lot of a neighboring nightclub.

“I saw children, pregnant women, senior citizens and young people,” Velazquez said. “It’s horrific.”

Officials said rescue efforts were hampered by fears that the cube-shaped building, which occupies much of a city block, might collapse.

Local television network Telefuturo reported that after some shoppers on the floors above the fire took advantage of the initial confusion to steal, one or several managers or security guards sealed some exits

Julio Gimenez, an attorney for the market’s owners, denied the charge. “Nothing was closed,” Gimenez said. “Everyone who could escape this unfortunate event did.”

But witnesses described neighbors scrambling to break open locked doors to allow those inside to escape.

The bodies of dozens of dead are covered in a yard in front of the burning Ycua Bolanos supermarket in Asuncion, Paraguay. The fire broke out in the store while it was crowded with Sunday midday shoppers.

“A group of us went to break all these windows with rocks,” one man told Telefuturo, pointing to a series of street-level glass doors pockmarked with holes. “We got a lot of people out that way.”

Daniel Paiva, one of the owners of the complex, granted a television interview moments after escaping the burning building. “It was so fast,” he said of the fire. “Everything happened in a few minutes.”

Paiva, too, said no doors were locked. Later Sunday, Paraguayan authorities detained him for investigation of charges of “culpable homicide.” Authorities would not reveal where he was held because they feared he might be attacked by relatives of the victims.

Firefighters took many of the dead to the temporary morgue at a nearby nightclub, where reporters counted some 111 bodies lined up in a parking lot Sunday afternoon, many burned beyond recognition.