Los Angeles, California - A powerful earthquake struck Thursday off the coast of California, sparking a tsunami warning, US seismologists said.

The 7.0-magnitude quake was recorded at a depth of just six miles, almost 62 miles west-southwest of Ferndale, according to the US Geological Survey.

"Based on preliminary earthquake parameters... hazardous tsunami are possible for coasts located within 300 KM of the earthquake epicenter," said a warning issued by the National Weather Service's Tsunami Warning Center in Honolulu.

The warning noted that no areas had yet experienced any waves, but that anyone near a coastline should be alert to the possibility of danger.

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Smartphone users received warnings urging them to move to higher ground immediately, the San Francisco Chronicle reported.

"A series of powerful waves and strong currents may impact coasts near you," the warning said. "You are in danger. Get away from coastal waters."

The paper said tsunami warning sirens were activated along a stretch of the coast, including in Bonny Doon in Santa Cruz County.

The USGS, which monitors seismic activity, said the quake struck at 10:44 AM local time.

Media reports suggested that the quake had been felt across the region, including in the Bay Area, where some people said they had felt strong shaking and rolling waves underfoot.