PYRAMID LAKE (CBSLA.com) — A portion of the southbound Interstate 5 was closed Tuesday after a collision involving two big rigs sparked a brush fire near Castaic.

The accident occurred around 6 a.m. near Smokey Bear Road.

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One of the big rigs engulfed in flames, which sparked a brush fire, officials said.

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One driver was pronounced dead at the scene, and the other was transported to a local hospital in unknown condition.

A SigAlert was issued shutting down all lanes south of Smokey Bear Road. One lane was reopened around 7:30 a.m., according to the California Highway Patrol.

“We’re asking the motorists to take the alternative route, which is the 138 to the 14 until we can open up that freeway,” CHP Officer Kevin Tao said.

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The cause of the collision was under investigation.