A deluge of rain in recent burn areas of Southern California caused mudslides, destroyed homes and wreaked havoc on communities from Santa Barbara to Los Angeles counties, leaving at least 15 people dead as of Wednesday morning.

The deaths were in southern Santa Barbara County, where a devastating wildfire recently left charred hillsides without vegetation cover to hold the rainfall.

The county sheriff's department said the fatalities were in the Montecito and Carpinteria communities, where the Thomas fire recently burned. Crews were also looking for missing people.

On Wednesday morning, around 300 people remained stranded in the Romero Canyon area of Montecito, and rescue efforts were underway to get to them.

"We're still doing active search and rescue in areas impacted," Yaneris Muniz, a spokesperson for the Joint Information Center in Santa Barbara, told CNBC on Wednesday morning. "There are families calling us about individuals who are missing — about a dozen to two dozen."

For more photos, see Fire and rain: Mudslides now sweep across Santa Barbara County after devastating wildfires

"At least several dozen homes ... have either been destroyed or severely damaged — and likely many other ones ... are in areas that are, as yet, inaccessible," Santa Barbara County Sheriff Bill Brown said Tuesday.

Weather forecasters had predicted some of the heaviest rain could fall in areas where the Thomas and Creek fires recently burned. Portions of those communities were under a mandatory evacuation but the deadly mudslides struck some areas that were not included in the order.

The National Weather Service recorded more than 5 inches of rain north of Ventura County's Ojai community in the Thomas fire burn area. Also, more than 3 inches of rain was collected at weather stations in Santa Barbara County.

At least 25 people have been injured and 50 rescued due to the storm, including to children, according to Santa Barbara County officials.

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Santa Barbara fire crews started rescues early Tuesday from floodwaters and mudflows in the Montecito area, 85 miles northwest of Los Angeles, where multimillion-dollar homes owned by celebrities are located. The water swept several homes in the community from their foundations.

Helicopters were used to evacuate people trapped in hillside areas of Santa Barbara County where heavy rain made some roads impassable due to flooding.

A Coast Guard spokesman in Los Angeles confirmed it deployed three helicopter crews Tuesday to help local authorities with rescues in the Montecito, Summerland and Carpinteria areas.

One of the rescues involved airlifting two burn victims from a home explosion in Montecito to a Santa Barbara-area hospital. The storm-related explosion was believed to be caused by a severed gas line.

A later rescue involved helping two people and a dog from a rooftop.

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Among other rescues was a 14-year-old girl who had been trapped inside a home that got swept off its foundation, according to Mike Eliason, a spokesman for the Santa Barbara County Fire Department .

"The house came to rest up against trees," said Eliason. "She was trapped in there for hours. It took firefighters two hours to cut her out of the house. They just finally rescued her and brought her out."

Parts of the busy U.S. 101 freeway that connects Santa Barbara with Ventura remained closed Wednesday due to debris and mud left by overflows from Montecito Creek.

Flooding debris also swamped the Montecito Inn.