As many as 13 people are reported dead amid “knee-deep” mudslides in Southern California triggered by heavy rains and flash floods.

More than 160 people have been taken to hospital. Twenty had “storm-related injuries” and four were critically hurt.

The bad weather forced the closure of several theme parks, including Six Flags Magic Mountain in Valencia and SeaWorld in San Diego.

A group of up to 300 people are reportedly trapped in Romero Canyon, east of Santa Barbara.

Santa Barbara County Sheriff Bill Brow said the scene “looked like a World War I battlefield”.

He added: “It was literally a carpet of mud and debris everywhere, with huge boulders, rocks, down trees, power lines, wrecked cars – lots of obstacles and challenges for rescue personnel to get to homes.”

The mud was “knee-deep” in many places on the roadways and even deeper in the canyons, Brown said.

The flooding and mudslides, affecting areas scorched by wildfires last month, have shut down more than 30 miles of the main coastal road.

Emergency services said a number of people were unaccounted for and they expected the number of deaths to rise, the BBC reported.

Thousands fled the deluge and more than 50 rescues have been performed.

The hardest-hit homes were those that were not in the evacuation zone, officials say.