At least 18 people have been confirmed dead in mudslides in California, as officials admit the window is closing for other survivors to be found alive.

Authorities believe five people are still missing, aged between two and 30. Four children are among the dead, including a three-year-old girl who died alongside her mother.

Mandatory evacuations have been extended as more than 1,200 emergency workers continue to search mud as deep as 15ft (4.6m) in places. Drones, military vehicles and search dogs have been brought in to help with rescue and clean-up efforts. “We’ve got a window that’s closing, but we’re still very optimistic. There’s been plenty of cases where they’ve found people a week after,” Santa Barbara County Fire Department spokesman Mike Eliason said.

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Uncertainty remains around the exact number of people still missing, as authorities warned the figure may continue to fluctuate. On Thursday they believed dozens were unaccounted for, but the number was revised down. A mandatory evacuation order has been extended, as Santa Barbara’s County Sherriff said residents staying behind were hindering recovery efforts. Gas and electricity supplies are expected to be cut off in the area on Saturday.