Authorities investigating cause of fire and explosion that injured 3 in downtown L.A.

Authorities on Sunday were still trying to determine the cause of an explosion and fire in an industrial area of downtown Los Angeles this weekend that left three people injured, including two critically.

Witnesses said they heard a loud “boom” around 12 p.m. Saturday in the building at 743 Kohler St. The explosion crumpled the building, which erupted into a fireball, sending a plume of black smoke hundreds of feet into the air that could be seen for miles.

Dozens of firefighters arrived on the scene to find the building fully engulfed in flames. Much of the 50-foot-by-100-foot one-story building was destroyed. Video of the fire shows flames jumping to neighboring businesses.

It took firefighters about an hour to extinguish the blaze, according to the Los Angeles Fire Department.

Two of the injured men were taken to a local hospital and were listed in critical condition with severe burn injuries, officials said. A third man suffered unspecified injuries and was transported in fair condition, according to authorities.

Investigators are still trying to determine the name of the business and the contents of the building.

Brian Humphrey, a spokesman for the fire department, said authorities would talk to the victims to help determine the circumstances surrounding the fire. But because of the extent of their injuries that might take awhile.