More than 100 homes were destroyed, and another 300 have been damaged.
More than 50 people have been rescued from rooftops after trees and power lines blocked roads.
A 14-year-old girl was also rescued from the mud after being trapped for hours.
Footage Oprah shared on the site included flames that were burning due to a nearby gas leak, while another video showed the star walking through her backyard with wellington boots on. "Praying for the survivors and preparing for whatever may come", said Lowe on Twitter.
Winfrey, 63, took to Instagram to share photos and videos of her home in Montecito, Calif., which has been damaged by the natural disaster. The Catholic school's headmaster Michael van Hecke said Mr Rohter's wife had been injured in the mudslide.
"It's just waiting and not knowing, and the more I haven't heard from them - we have to find them", said Kelly Weimer, whose elderly parents' home was wrecked by the torrent of mud in a coastal town in Santa Barbara.
None of those killed have been publicly identified yet, with Santa Barbara's County Sheriff Bill Brown telling reporters: "We realise this is going to be a long and hard journey for all of us and our community".
The death toll wrought by storms and flooding in southern California continues to rise, with officials reporting late Wednesday that they'd found the bodies of two more mudslide victims. The fires burned away grass and shrubs that hold the soil in place and also baked a waxy layer into the earth that prevents water from sinking deeply into the ground. "Looking for missing persons", she wrote.
People in Montecito avoided the ravages of the biggest wildfire in California history last month.
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