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A nearly 400-acre brush fire near Castaic prompted a SigAlert and complete closure of both directions of the 5 Freeway Saturday afternoon, officials said.

The fire, dubbed the Route Fire, reached 392 acres as of 6:28 p.m., according to the Angeles National Forest. It was 140 acres as of 6:05 p.m.

As of 9:09 p.m., two lanes were opened in both directions, according to Cal Trans, but motorists were advised to avoid the area if possible.

The Route Fire was threatening structures, according to the Los Angeles County Sheriff’s Department Santa Clarita Valley station.

The southbound 5 Freeway was closed at Vista Del Lago Road and the northbound lanes closed at Templin Highway, according to the California Highway Patrol.

The fire is being handled by the Los Angeles County Fire Department, which is utilizing water drops from helicopters.