LOS ANGELES, Jan. 9 (Xinhua) -- At least 13 people have been killed in the southern California mudslides caused by a winter storm and the death toll is likely to increase, Santa Barbara County Sheriff Bill Brown told a news conference on Tuesday.

"While we hope it will not, we expect that this number will increase as we continue to look for people who are still missing and unaccounted for," Brown said.

Emergency services, using search dogs and helicopters, are still on the site looking for victims, he said.

He did not say how many people could be trapped.

Strong winter storm on Monday hammered southern California on the U.S. West Coast with heavy downpours, triggering deadly mud flows before dawn on Tuesday.

TV footages from local media show that in the Montecito area, northwest of Los Angeles, the mudslides toppled trees and swept cars away. Multiple houses in the region were torn from their foundations.

Some 500 firefighters from all across the country are continuing to engage in rescue operations, the sheriff said.