EUREKA, Calif. - A pair of minor-to-moderate offshore earthquakes have struck the northern California coast, but there are no reports of any damage or injury.

The U.S. Geological Survey says in a preliminary report that the first quake had a magnitude of 5.1. It struck at 2:27 a.m. Sunday about 330 kilometres northwest of Sacramento at a depth of 18.5 kilometres.

The second was a magnitude 4.1 quake that struck one minute later farther south, about 120 kilometres northwest of San Francisco at a depth of about five kilometres.

Sheriff's dispatchers in the nearest affected counties of Humboldt and Sonoma say they've received no word of injuries or damage.