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LOS ANGELES — With thick plumes of smoke, towering flames and mass evacuations, a fast-moving wildfire struck one of America’s major cities on Wednesday.

As fires raged out of control across Southern California, a new blaze erupted in the Bel-Air neighborhood of Los Angeles, near iconic landmarks like the U.C.L.A. campus and the Getty Museum, home to old masters paintings and ancient Roman statues.

It burned up to the edges of the 405 freeway, the nation’s busiest highway carrying about 400,000 vehicles a day, where the northbound lanes were closed for much of the day and commuters drove through a shower of ash with flames rising in the horizon.

Forty miles to the northwest, the largest of several fires underway had consumed 90,000 acres by Wednesday night and at least 150 structures — probably hundreds more, fire officials said — and threatened 12,000 others in the city of Ventura and neighboring communities, and was 5 percent contained. Other major fires were burning in the northern San Fernando Valley and the rugged region north of Los Angeles.