The death toll from the devastating mudslides that struck Southern California rose to 17 on Thursday night as rescue crews combed affluent Santa Barbara for up to two dozen people still missing.

Searchers picked their way across a landscape strewn with boulders and covered shoulder-high in places with mud the consistency of wet cement in their hunt for the missing.

“Right now our assets are focused on determining if anyone is still alive in any of those structures that have been damaged,” Santa Barbara County Sheriff Bill Brown said.

Rescue crews with dogs and thermal-imaging equipment were searching the hills around Santa Barbara after rain-driven mudslides swept through the coastal community.

“It’s just waiting and not knowing, and the more I haven’t heard from them – we have to find them,” Kelly Weimer, whose elderly parents’ home was wrecked by the mudslide told the Associated Press.

Mudslides damaged historic hotels and the homes of celebrities including Oprah Winfrey, who relish the area sandwiched between the ocean and the sprawling Los Padres National Forest for its natural beauty and proximity to sprawling Los Angeles.

But the wooded hillsides that once gave their estates a sense of seclusion were largely denuded by last year’s historic wildfires, setting the stage for the massive slides that slammed into homes, turned highways into raging rivers and shredded cars into nearly unrecognisable tangles of metal after heavy Tuesday rains.

Between 12 and 24 people who were believed to in the area at the time of the slides remained unaccounted for, said Chris Elms, a spokesman for state firefighters.

Some 300 people were trapped in the Romero Canyon area of Montecito because debris was blocking their way out of the neighbourhood, Santa Barbara County spokeswoman Yaneris Muniz said.

About 500 law enforcement officers and firefighters were combing mud-covered neighbourhoods, using dogs, helicopters and thermal imaging equipment to locate missing people.

Officials have ordered residents in a large swath of Montecito to stay in their homes so that rescuers can better go about their work.

About 300 people were stranded in a canyon. Local rescue crews, using borrowed helicopters from the US Coast Guard, worked to airlift them out, officials said.

– With agencies