The epicenter of the quake hit just north of the coastal town of Cambria, about 200 miles northwest of Los Angeles, reports CBS News Correspondent Elizabeth Sanchez.
The quake struck at 11:16 a.m. The U.S. Geological Survey gave it a preliminary magnitude of 6.5, dynamic enough to sway high-rise buildings from L.A. to San Francisco and send tremors across a wide swath of the central coast. The quakes' effects ranged from strong shaking to slow-rolling waves.
The bodies of two people were pulled from the rubble of a building in downtown Paso Robles, said Terry Minshull of the Paso Robles Fire Department. He said the victims were people missing from a nearby store.
Firefighters searched debris along a block of collapsed buildings in the town of 25,000 about 20 miles east of the epicenter. Cars were crushed by the debris.
Several people were also reported hurt by falling barrels at a winery, San Luis Obispo County authorities said.
"Everything else seems to be little things, like medical aid and some gas leaking," said fire information spokesman Gilbert Portillo.
The main shock was immediately followed by at least five aftershocks of magnitude larger than 3.3. The biggest was estimated at 4.7.
Cambria is in San Luis Obispo County, which has a population of around 250,000.
"It was pretty sharp," said Sharyn Conn, receptionist at the oceanside Cypress Cove Inn in Cambria. "It really went on and on. I just got everyone under the door frames and rode it out."
The site is only a few miles from San Simeon, William Randolph Hearst's castle. The popular tourist attraction was evacuated as a precaution but reported no major damage.
In Paso Robles, TV images showed the buildings slumped but still standing amid debris.
The quake struck on a series of faults that run parallel to the San Andreas Fault, said Lucy Jones, scientist in charge of the U.S. Geological Survey office in Pasadena. The quake probably ruptured along roughly 20 miles of a yet-unknown fault, Jones said.
"It's luckily on the coast — there is not very much nearby. That's a good thing," she said.
The last one of a similar size in the area was in 1952, said Ross Stein of the USGS in Menlo Park.
San Luis Obispo County sheriff's Sgt. Pete Hodgkin said damage reports were trickling in.
"It's the usual stuff, broken glass and stuff. Haven't heard anything serious," Hodgkin said. "Some people are hurt at the Wild Horse Winery, some wine barrels fell over. I don't know anything more.
"It's kind of hectic," he said. "It felt like a big one, like the San Francisco earthquake years ago. The lights went out. We're on emergency power here."
John Nelson, a spokesman for Pacific Gas and Electric, said about 10,000 homes and businesses were without power in the San Luis Obispo area.
The utility reported no major damage at its Diablo Canyon nuclear power plant; it was being checked for minor damage. Another utility, Duke Energy, said there was no substantial damage at its two coastal power plants, Morro Bay and Moss Landing.
Hearst Castle reported no obvious damage and no injuries, said Roy Stearns, spokesman for the state Department of Parks and Recreation. A crew was to go over its 150 rooms in detail; the only damage found immediately was a blown transformer at a campground, Stearns said.
The castle is particularly popular this time of year because it is decorated with the Hearst Christmas ornaments.
"People come from far and wide to see that, because it's pretty spectacular," Stearns said.
According to callers on local news radio in Fresno, the earthquake also was felt throughout the San Joaquin Valley.
Superintendent Pamela Martens of the Coast Unified School District in Cambria said school had been closed for the holidays, but there are "things off the shelf and all over the place. Computers are down."
A magnitude-6 quake can cause severe damage under a populated area, though damage is often much less in places with strong building codes.