Evacuation orders and evacuation warnings have been issued in some parts of Los Angeles, Ventura, Santa Barbara and Orange counties as life-threatening flooding hits the region, trapping people in cars and forcing residents to evacuate their homes.

In Los Angeles’ Baldwin Hills neighborhood, about six cars crashed while heading down a hill where the road was partly covered with mudslide debris, according to Los Angeles police. Multiple people were injured and one person might have suffered a broken leg, police said.

In San Bernardino County, three people were trying to drive across a flooded road when the car became submerged, according to the San Bernardino County Fire Department. The three people clung to a tree and were rescued, officials said.

In Los Angeles’ Studio City neighborhood, firefighters rescued 16 residents after debris flow damaged homes, the Los Angeles Fire Department said. No one was injured, officials said.

Two people have been killed by fallen trees during the powerful California storm.

A tree fell on a house in Boulder Creek on Sunday, killing one resident inside, according to the Santa Cruz Sheriff’s Department. A second person managed to escape the home, authorities said.

The second fatality was in Yuba City. An 82-year-old man was in his backyard on Sunday when he was killed by a falling redwood tree, Yuba City police said.

More than 516,000 customers in California are waking up without power Monday morning as a powerful rainstorm slams the state.

Flash flood warnings and flood advisories are in effect for parts of Los Angeles and Ventura counties.

Los Angeles recorded more than 4 inches of rain on Sunday, beating the city's daily record of 2.55 inches set in 1927.

The relentless rainfall and life-threatening flooding are ongoing across the Los Angeles area on Monday morning and will continue throughout the day.

A flash flood warning is in effect from Malibu to Beverly Hills to Brentwood to Hollywood to Burbank.

By Tuesday morning, the heaviest rain will be targeting areas east of San Diego.

On Tuesday afternoon, scattered downpours continue throughout California, and by Wednesday, just a few light showers and sprinkles will remain.

A storm system continues to slam Southern California, with an atmospheric river bringing a plume of moisture all the way from the tropical Pacific Ocean.

The National Weather Service has flood watches in effect Tuesday morning for California as well as Nevada and Arizona. Winter storm warnings and snow alerts were also in effect for nine western states, from Montana to California, as this storm spreads into the Rocky Mountains.

As of early Tuesday, up to 3 feet of snow had already fallen on the Sierra Nevada mountain range.

The threat of flash floods on Tuesday will be mostly from Los Angeles to San Diego in California and from Yuma to Phoenix in Arizona. Locally, less than 1 inch of rain is in the forecast for Los Angeles, but the foothills around the city could get an additional 1 to 2 inches of rain.

On Wednesday, another storm system -- much weaker -- is expected to move through California from the San Francisco Bay Area to Los Angeles by the evening hours. The storm could dump an additional 1 inch of rain on southern California.

-ABC News' Max Golembo