The fire seemed calm on Sunday before gusts kicked up the flames that tore through neighbourhoods in Lower Lake, a town of 1,200 about 90 miles north of San Francisco, officials said.
It reached Main Street and burned the post office, a winery, a Habitat for Humanity office and several businesses as thick, black smoke loomed over the small central strip.
Staff at a hospital in Clearlake, a neighbouring town of about 15,000, rushed to transfer 16 patients to another hospital and firefighters carried goats and other animals to safety as homes burned around them.
The blaze was one of 11 large wildfires in California, where high temperatures and parched conditions brought on by a five-year drought raised the fire danger. In central California, a day-old wildfire burned 20 structures and threatened 150 homes.
The Lower Lake fire broke out on Saturday afternoon and exploded to nearly five square miles as it fed on bone-dry vegetation.
Besides the wind, 100F (37C) heat hindered firefighters struggling to get a handle on the largely out-of-control blaze.
“This fire roared through the city like a wave of water - it was a wave of fire that came through here,” said Lt Doug Pittman, a Marin County sheriff’s spokesman working on behalf of the California Department of Forestry and Fire Protection.
Well over 100 homes were destroyed, Cal Fire spokesman Daniel Berlant said. Officials did not immediately know how many businesses and other buildings were lost but say thousands are still threatened.