EVACUATIONS HAVE BEEN ordered in high-risk coastal areas of California as a huge storm bears down on the state.

California Governor Gavin Newsom declared a state of emergency to allow for a quick response and to aid in clean-up from another powerful storm that hit just days earlier.

The new storm already left more than 76,000 customers in the San Francisco Bay Area and nearly 19,000 more along the Central Coast without power.

Dozens of flights out of San Francisco were cancelled, and schools in one of the city’s suburbs pre-emptively cancelled classes.

Officials warned people throughout Northern California to stay off the roads.

“We anticipate that this may be one of the most challenging and impactful series of storms to touch down in California in the last five years,” said Nancy Ward, the new director of the California Governor’s Office of Emergency Services.

The storm, which brought howling winds to Northern California yesterday evening, is one of three so-called atmospheric river storms in the last week to reach the drought-stricken state.

In Southern California, the storm was expected to peak in intensity overnight, with Santa Barbara and Ventura counties likely to see the most rain, forecasters said.

The first evacuations were ordered for those living in areas burned by three recent wildfires in Santa Barbara County, where heavy rain forecast for overnight could cause widespread flooding and unleash debris flows.

County officials did not have a firm number for how many people were under evacuation orders, but Susan Klein-Rothschild, a spokesperson in the county’s emergency operations centre, estimated it was in the hundreds.

Among the towns ordered to evacuate was Montecito, where five years ago huge boulders, mud and debris swept down mountains through the town to the shoreline, killing 23 people and destroying more than 100 homes.

“What we’re talking about here is a lot of water coming off the top of the hills, coming down into the creeks and streams and as it comes down, it gains momentum and that’s what the initial danger is,” Montecito Fire Department chief Kevin Taylor said.

Elsewhere, a 45-mile (72-kilometre) stretch of the coastal Highway 1 that runs through Big Sur was closed on Wednesday evening in anticipation of flooding and rock falls.

Further north, a 25-mile (40-kilometre) stretch of Highway 101 was closed due to several downed trees.

Officials asked drivers to stay off the roads unless absolutely necessary — and to stay informed by signing up for updates from emergency officials about downed trees and power lines, and flooding.

The storm was forecast to drop up to 10 inches (25.4 centimetres) of rain on an area where the hills have already been saturated over the past month.