L.A. firefighters search for missing people in Sylmar explosion [Updated]

Los Angeles firefighters were launching a search-and-rescue operation Tuesday evening after a huge explosion tore through a Sylmar commercial building, seriously injuring at least four people.

An unknown number of occupants were believed to be missing inside the structure at 12349 Gladstone Ave., said Capt. Jamie Moore of the Los Angeles Fire Department.

[Updated 5:06 p.m.: The Fire Department is now saying that two men were seriously injured and that a third person suffered minor injuries.]

Firefighters discovered a ruptured natural-gas line near the explosion scene but said they had yet to established what sparked the blast, which was reported about 4:40 p.m.

"As of right now," Moore told The Times, "we don't know what caused it."

A nearby business owner said he heard a "massive explosion."

"We ran outside and saw two guys badly hurt," said the owner, who declined to be identified during a telephone interview. "There was a lot of chaos."

Firefighters have not identified the business.

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Map shows location of the explosion. Credit: Google Maps.