By CNN

(CNN) A day after mudslides crushed several Southern California homes and left at least 15 people dead, rescuers faced a difficult task Wednesday as hundreds of people remain cut off by debris in one neighborhood and others are still missing, officials said.

Heavy rains early Tuesday caused rivers of mud and debris to run down from hillsides in Santa Barbara County, demolishing homes in the seaside community of Montecito just weeks after a massive wildfire scarred the region.

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

"We can't get to them, and they can't get to us. ... Once we have daybreak, you will see helicopters start rescuing people there," Muniz said.

Latest developments

• Deadly storm: The 15 deaths were reported in Santa Barbara County, authorities said.

• More missing: Muniz said it's unclear how many people are missing, but searches are ongoing. Earlier, officials said at least two dozen people were unaccounted for.

• Hundreds of calls: As the storm hit hard between 3 and 6 a.m. Tuesday, sheriff's office dispatchers handled more than 600 phone calls for assistance, Santa Barbara County Sheriff Bill Brown said.

• Road closed: US 101 in parts of Montecito and Santa Barbara will remain closed for at least 48 hours, authorities said Tuesday.

• Intense rain: By Tuesday, more than 5.5 inches of rain had fallen in parts of Ventura County over two days, the National Weather Service said. In Carpinteria, nearly 1 inch fell in 15 minutes, the agency said.

A police vehicle drives across a flooded side road near the San Ysidro exit of US 101 in Montecito on January 9.

'River of mud'

Thomas Tighe told CNN affiliate KCAL he was outside his Montecito home and heard "a deep rumbling, an ominous sound I knew was ... boulders moving as the mud was rising."

He saw two cars moving sideways down the middle of the street "in a river of mud."

Peter Hartmann said the destruction was everywhere.

"There were gas mains that had popped, where you could hear the hissing," he told the TV station.

"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."

Before the storm hit, Santa Barbara issued mandatory evacuations for 7,000 people, including in parts of Carpinteria, Montecito and Goleta, which are below areas scorched by wildfires, county spokeswoman Gina DePinto said.

"While some residents cooperated with the evacuations, many did not. Many chose to stay in place," said Brown, the sheriff.

Sheriff deputies spent Monday conducting door-to-door evacuations for 7,000 people in a mandatory evacuation area. But the area where homes were destroyed, south of Highway 192, was not in a mandatory evacuation zone.

Rescue personnel still have areas to search, Brown said.

"It was literally a carpet of mud and debris everywhere, with huge boulders, rocks, (downed) trees, power lines, wrecked cars -- lots of obstacles and challenges for rescue personnel to get to homes," Brown said.

'Mud came in an instant'

Ben Hyatt said a river of mud crashed through a neighbor's house in Montecito, a community of about 8,000 east of Santa Barbara.

"Apparently, one of their cars ended (up) in their backyard. We have neighbors at (the) top of the street that evacuated to their roof," Hyatt said.

Hyatt said his Montecito house was "surrounded by mud," and a washing machine had drifted into his front yard.

Debris litters the area near Hyatt's home Tuesday in Montecito in Santa Barbara County.

"Mud came in an instant, like a dam breaking. (It) surrounded the house, 2 to 3 feet," he said.

More than 1 inch of rain per hour

The rain fell at more than 1.5 inches per hour at one point early Tuesday in parts of Southern California. About a half inch per hour is enough to start mudslides, said Robbie Monroe of the National Weather Service in Oxnard.

The downpour fell in areas charred by recent wildfires, which burned vegetation that otherwise could make the terrain flood-resistant.

The Thomas Fire -- the largest wildfire in California's recorded history -- has burned more than 281,000 acres in Santa Barbara and Ventura counties since it began in early December. It was 92% contained, and officials don't expect full containment until later this month.

Montecito and Carpinteria are especially vulnerable to mudslides because the steep terrain in some places goes from thousands of feet above to sea level to sea level in "a matter of just a few miles," said Tom Fayram, a deputy public works director with Santa Barbara County.

"That's definitely at play here. It's just a mess," he said.

Mudslides are not uncommon to the area and can be deadly. In January 2005, a landslide struck La Conchita in Ventura County, killing 10 people.

CNN's Jason Hanna, Stella Chan, Paul P. Murphy, Jason Kravarik and Judson Jones contributed to this report.