SEARCH and rescue efforts have intensified for hundreds of Montecito residents feared trapped in their homes after deadly walls of mud and debris roared down California hillsides stripped of vegetation by recent ferocious wildfires.

The one-two punch of fire and downpour-fuelled debris flows have debilitated the affluent, picturesque community of about 10,000 people. The slides have killed at least 17, destroyed an estimated 100 homes, and sent rescuers scrambling through the rubble searching for dozens who are missing.

“We have no idea where they’re at," Santa Barbara County spokeswoman Amber Anderson said of the missing people. "We think somewhere in the debris field."

Sheriff Bill Brown said the primary focus of first responders was "to evacuate those who are trapped and need help getting out." He said residents can shelter in place in their homes — adding that anyone moving about the area faces possible arrest.

The county fire department tweeted a photo of a mud-encased 14-year-old girl being rescued alive from the rubble of a Montecito home. Fire spokesman MIke Eliason said the girl had been trapped for hours.

Scores of homes have been destroyed or severely damaged, with search efforts focused on determining if their residents survived. Sheriff deputies and other first responders had to cautiously pick through debris to access shattered homes.

Helicopters, rescue dogs and swift-water rescue teams were aiding the search, which was slowed by closed roads and downed trees and power lines.

Numerous celebrities have homes in the area. Actor Rob Lowe said on social media that Oprah Winfrey's home was being used as a staging area for helicopter rescues.

"Mourning the dead in our little town tonight," Lowe said. "Praying for the survivors and preparing for whatever may come. #Montecito."

Winfrey posted a photo of mud in her backyard. "What a day!" she said, adding "Helicopters rescuing my neighbours. Looking for missing persons."

Ellen DeGeneres tweeted a photo of the debris-strewn street, adding that she didn't know the fate of her home.

"I’m heartbroken for our community of Montecito," she said. "I’m devastated for the families who lost loved ones. I’m grateful to all the rescue workers. Please send love to Montecito."

Ellen DeGeneres tweeted a photo of the debris-strewn street, adding that she didn't know the fate of her home.

"I’m heartbroken for our community of Montecito," she said. "I’m devastated for the families who lost loved ones. I’m grateful to all the rescue workers. Please send love to Montecito."

Much of the area was devastated by recent wildfires, including the massive Thomas fire, the largest in California history. The blaze burned more than 440 square miles and more than 1,000 homes, businesses and other buildings in the area last month.

Then, this week, it started to rain. Hillsides stripped of their vegetation by the fires were defenceless as mud, boulders and other debris were swept down onto roads and communities.

U.S. Highway 101, a crucial link between Ventura and Santa Barbara, was so overwhelmed by mud and debris that authorities announced it will remain closed until at least Monday.

Dozens of boulders sat atop muddied tree branches where at least three homes once stood on a Montecito street as rescuers continued to search for the missing.

The only remnants of the homes on Olive Mill Road were the faint traces of their foundation and the neighbours that knew of them.

"It happened that quickly. It wasn't a trickle," said William Johnston, who lives in a retirement community down the street.

The first significant rain Santa Barbara County saw after the Thomas fire left hillsides without brush triggered mudslides and other debris flow early Tuesday that ran a path of destruction through the neighbourhood.

A wall of water carrying uprooted trees and boulders moved like a river through the residential street.

Residents waded through mud and still-flowing water to get to their homes. Some had to hop onto the roof to get inside through an upstairs window.

They were assisted by firefighters and search-and-rescue teams who continued to try to account for the missing.

The sound of working construction equipment could be heard nearby as backhoes dug up the debris. One such piece of equipment grabbed a piece of a car.

A bevy of trucks from Southern California Edison were working at what was once a small, triangular-shaped park across the way from the retirement community.

Some residents watched as crews tried to clean up the area, still in disbelief.

One such resident, Marco Farrell, 45, called the slide more frightening than the "biggest, scariest, horrifying monster you've ever dreamed of."

The worst of the rainfall occurred in Montecito in a 15-minute span before dawn Tuesday.

“All hell broke loose,” said resident Peter Hartmann. “Power lines were down, high-voltage power lines, the large aluminum poles to hold those were snapped in half. Water was flowing out of water mains and sheared-off fire hydrants.”