Los Angeles, Dec 21 (DPA) A weather system that occurs only once every 10 or 15 years is pounding southern California with record rainfall and could cause massive mudslides as it continues through the week, meteorologists said Monday.

Downtown Los Angeles was pelted with more than 7 centimetres of rain, its heaviest rainfall since 1921, and in the past four days alone has received a quarter of its average annual rainfall, according to the National Weather Service.

The southern California ski resort of Mammoth Mountain was inundated with some 3 metres of snow, while in northern California, ski resorts such as Squaw Valley had so much snowfall that they had to close the lifts on what is normally one of the busiest weekends of the year.

Damage has so far been limited to downed trees and power lines, isolated flooding and an increase in car accidents. But after a small lull Monday the warm Pacific storm was expected to continue dumping rain and high winds across California, as it moved east and threatened the east coast with a white Christmas next weekend.

Such storms are highly unusual according to Bill Hoffer, spokesman for the National Weather Service in Oxnard.

Normally, a region of high pressure over the central Pacific Ocean deflects storms away from California and into Oregon and Washington states further to the north. But that pressure has weakened, allowing moist, warm Pacific storm systems to stretch from Asia through Hawaii into California. Such a weather pattern pops up once every 10 to 15 years, he said.