Heart-stopping pictures show three mega-mansions in the city of Dana Point apparently now perilously close to the Pacific Ocean following the rockfall.

But astonishingly, the properties are still livable, with engineers assuring owners that their homes are in no danger of sliding into the sea.

Lewis Bruggeman, who owns one of the homes in the tony enclave south of Los Angeles, told a local broadcaster his home is "not threatened and it will not be" labelled uninhabitable.

"The city agrees that there's no major structural issue with the house right now," he told KCAL-TV.

The landslip came after California was battered by powerful storms that dumped billions of gallons (liters) of rain, sparking localized flooding and travel disruption.

Before-and-after pictures published by the Los Angeles Times show a large area of greenery behind Bruggeman's $16-million home has effectively vanished.

AFP photos show lighter sand and soil that has been exposed with the tumbling of the darker cliff face, with chunks of greenery in the new crater.

Dana Point officials say while the pictures are dramatic, there is no immediate danger.

"Engineers who already surveyed the home said there was no damage and there is no imminent threat to the structure, which is really good news," Dana Point Mayor Jamey Federico said, according to the Times.

"So quite frankly, it looks a lot scarier than it really is."

Heavy rains across southern California last week sparked more than 500 landslides of varying sizes in Los Angeles alone.

Forecasters say the area is in line for another soaking over the coming days.