At least 15 people have been killed after the first major storm to hit southern California this winter unleashed flooding and mudslides that toppled homes and prompted emergency rescues and evacuation orders in an area that just endured historically intense wildfires.

Long-awaited rain fell on a region left vulnerable to new forms of natural disaster after spending weeks ablaze, the type of pivot from weather hazard to weather hazard that is common to a state that periodically grapples with drought, flooding, earthquakes and wildfires. By Tuesday morning, some places in the greater Los Angeles area had seen more than 10 centimetres (4 inches) of rainfall.

Those heavy rains brought severe and sometimes-deadly consequences, including what one official called a “catastrophic mud flow” that hurtled onto Highway 101 early in the morning. Officials in Santa Barbara said at least 15 people had died, with at least 25 others injured, a number poised to grow as search-and-rescue operations continued.

“It looked like a World War I battlefield. It was literally a carpet of mud and debris everywhere,” Santa Barbara County Sheriff Bill Brown said at a press conference, describing a landscape littered with boulders, mangled cars and downed powerlines.

Houses were swept away, stretches of major roads were rendered inaccessible by inundating mud and rain and and people were ordered out of their homes in areas that last month were menaced and forced to evacuate by raging blazes.

​Firefighters rescued scores of people who were trapped in vehicles and homes by water and debris, wading through waste-deep mud and avoiding downed wires. By the afternoon potentially dozens of people remained unaccounted for and first responders were at work evacuating hundreds of people trapped in a canyon.

“We still have an active search-and-rescue operation,” Mr Brown said, adding that “several dozen” homes were likely destroyed or severely damaged.

In Montecito, firefighters extracted a mud-coated 14-year-old girl from a collapsed home where she had been pinioned for hours.

“I thought I was dead for a minute there,” the girl could be heard saying on video posted by KNBC-TV before she was taken away on a stretcher.

Santa Barbara County spokesman David Villalobos told the Associated Press that all of the deaths were believed to have occurred in Montecito, a wealthy enclave of about 9,000 people northwest of Los Angeles that is home to such celebrities as Oprah Winfrey, Rob Lowe and Ellen DeGeneres.

California's Office of Emergency Services said it had deployed flood rescue teams to help pull people from the torrential cocktail of rainwater and mud.

“Teams are actively engaged in life saving operations,” the office said.

California mudslides: in pictures Show all 9 1 /9 California mudslides: in pictures California mudslides: in pictures Emergency personnel carry a woman rescued from a collapsed house REUTERS California mudslides: in pictures Mudslides unleashed by a ferocious storm demolished homes in southern California AFP/Getty California mudslides: in pictures Emergency personnel rescue a 14-year-old girl from a house Santa Barbara County Fire Department/Handout via REUTERS California mudslides: in pictures A car piled up in debris EPA California mudslides: in pictures Emergency personnel carry a man covered in mud REUTERS California mudslides: in pictures Emergency personnel evacuate local residents and their dogs through flooded waters after a mudslide in Montecito REUTERS California mudslides: in pictures A damaged vehicle that was pushed by mudflow onto the US 101 Freeway EPA California mudslides: in pictures Los Angeles Fire Department Firefighters work admist flood waters EPA California mudslides: in pictures A semi-tractor trailer sits stuck in mud Santa Barbara County Fire Department via AP

With several routes already shut down, authorities issued a shelter-in-place warning imploring people to avoid perilous roads.

“Take protective actions to stay safe which may include sheltering-in-place or seeking high ground, avoiding power lines and trees, staying off roads and highways, and do not attempt to leave and drive across flowing water or mud,” an alert warned.

Ellen DeGeneres posted a photo on Twitter of a roadway choked with mud and brown water.

“This is not a river,” DeGeneres wrote on Twitter. “This is the 101 freeway in my neighborhood right now. Montecito needs your love and support.”

Wildfires that scorched southern California for much of December — including an epic blaze that became the state’s largest — amplified the risk from winter storms, with fire-loosened soil threatening to surge forward when mixed with heavy rain.

Residents who spent much of last month being urged to stay off roads and warned of potential evacuation orders faced the same outcomes from a different cause.

Authorities in Santa Barbara County, north of Los Angeles, issued evacuation orders for areas that had burned — warning in an alert of “heavy rain, high winds and extremely dangerous flash flooding, mud and debris flows,” — and a local emergency declaration. The National Weather Service issued a flash flood warning for areas charred by a pair of recent wildfires.