Sinkholes swallowed cars and floodwaters swamped towns and swept away a small boy as the US state of California was wracked by more wild winter weather, while the next in a powerful string of storms loomed on the horizon.

Millions of residents faced flood warnings, nearly 50,000 people were under evacuation orders, and more than 110,000 homes and businesses were without power on Tuesday because of heavy rains, lightning, hail and landslides.

At least 17 people have died from storms that began late last month, Governor Gavin Newsom said.

The storm that began Monday dumped more than  45 centimetres (a foot and a half) of rain in Southern California mountains and buried Sierra Nevada ski resorts in more than 1.5 metres (five feet) of snow.

Rockfalls and landslides shut down roads, and gushing runoff turned sections of freeways into waterways.

Swollen rivers swamped homes and residents of small communities inundated with water and mud were stranded.

Raging waters crested the banks of Bear Creek and flooded parts of the city of Merced and neighbouring Planada, a small agricultural community along a highway leading to Yosemite National Park.

Neighbourhoods were under water with cars submerged up to their roofs.

Residents ordered to evacuate carried whatever they could salvage on their backs as they left in the rain.