A natural gas explosion in Los Angeles rocked a two story building Friday, throwing people into the street and killing at least one person. One other person in critical condition.

Firefighters were making sure the wreckage was safe before a rescue team was brought in with dogs to search. The building housed a commercial welding operation.

"They are shoring up any portions of the building that may be unsecured, ensuring that the beams aren't going to fall further," L.A. Fire Spokesman Eric Scott said.

Natural gas apparently sparked the blast but the building also contained flammable oxygen and acetylene, he said. The exact cause of the explosion is under investigation.