A magnitude-6.9 earthquake struck off the coast of Northern California Sunday night, the U.S. Geological Service reported.
The epicenter was 48 miles west-northwest of Ferndale and 50 miles west of Eureka at a depth of 4.3 miles, the USGS said.
The quake, which occurred at 10:18 p.m. PT (1:18 a.m ET), was initially reported as magnitude 6.1, but seismologists revised it upward to 6.9. It was followed by about a half-dozen aftershocks, including one of magnitude 4.6.
There were no reports of any damage or injuries though the quake was felt widely and strongly, according sheriff's and fire officials in Humboldt County, which includes most of the populated areas near the epicenter.
NBC Bay Area reported that police in Eureka said the shaking lasted 20 to 30 seconds.
Earthquakes are common in Eureka, a city of about 27,000 people about 270 miles northwest of San Francisco and 100 miles south of the Oregon state line.
The probability of a "strong and possibly damaging aftershock" of magnitude 5.0 or greater in the next seven days was 90 percent, the USGS warned, adding that there was a 5 percent to 10 percent chance of another quake as large as or larger than the initial one in the next week.
The Associated Press contributed to this report.