A deadly gas explosion obliterated an industrial building with such violent force Friday that a worker was hurled into the street, car windows were shattered and a survivor had his hair singed in the inferno.

One man died and another was critically injured in the blast that was blamed on a gas line that had been tampered with and rerouted.

Jonathan Apol, 20, a welder at a neighboring business, was putting on his work overalls when the explosion rocked the South Los Angeles street. He ran outside in his boxer shorts and saw the building engulfed in flames.

"It sounded like a plane had crashed in there," Apol said. "It was like a bang, then two seconds later, two more bangs."

Fragments of melting asphalt rooftop were sprayed across the street, and smashed floor tiles were hurled at least 50 feet from the metalworking business.

Apol said he saw two dazed men standing in front of the burning building. One was shouting the name of business owner Jaime Lara into the flames.

"He was just shouting his name ... but I don't think (he) responded," Apol said.

Daniel Ibarra, one of the dazed workers, said he had just taken some trash outside when the blast hit. The 27-year-old appeared in shock as he leaned against a wall with a bruised leg surveying the damage.

"I was very lucky," said Ibarra, whose thick black hair was singed.

The explosion blew one man across the street with severe burns. Firefighters could find no heartbeat and initially said he had been killed, but he was later revived at a hospital.

Another man died as he tried to move his stake-bed truck away from the building and was jolted by a downed 34,500-volt power line that had fallen on the vehicle, fire Capt. Stephen Ruda said.

Authorities did not immediately release the names of the two men.

The natural gas supply had been disconnected Thursday because the business was behind on its payments, Southern California Gas Co. spokesman Dennis Lord said.

To keep the gas flowing, someone had rerouted a pipe around the meter and a regulator designed to reduce gas pressure to safe levels.

"They were trying to start their business back up," Lord said.

Elizabeth Alvarado, a secretary at the metalworking business known as J.L. Spray, said it was owned by Jaime Lara.

The firm had four employees and made metal security fences, doors, windows and gates. It was nestled among a string of warehouses with corrugated-metal fronts.

After the flames were extinguished, shocked workers poured into the street and watched as fire crews sifted through debtis.

Josephina Perez, who works next door at a company that processes used clothing, said business owners looked out for each other in the blue-collar area.

The force of the blast blew in several ceiling windows in the 23,000-square-foot warehouse where she works.

"It was raining glass," she said. "It was so scary."