San Francisco: An earthquake with a magnitude of 6.5 was reported off the coast of Northern California on Thursday but there were no immediate reports of damage in the nearest town, officials said.

The quake was centered in the Pacific Ocean about 102 miles (165 kilometers) west of Ferndale, California, at a depth of 6.2 miles (10 km), the U.S. Geological Survey said.

The coastal area nearest the quake is sparsely populated.

There was no tsunami warning, advisory or threat in effect following the earthquake, the Pacific Tsunami Warning Center of the National Weather Service said on its website.

In Ferndale, which has a population of about 1,300 people, Mayor Don Hindley said in a phone interview that he had not heard of any damage from the quake. He said he felt the temblor for about 15 seconds.

"It wasn't that bad at all," Hindley said. He added that he felt more shaking from another quake earlier this week.

The area near Ferndale had a 4.3 magnitude earthquake right on the coastline on Monday, according to the USGS.

In Eureka, which is less than 20 miles (32 km) north of Ferndale, Twitter user Wanda Cloud reported that she felt a "jolt."

The Humboldt Bay Fire department in Eureka had received no calls related to the quake, said Ashleigh Jordan, administrative assistant at the department.

The quake was also felt at least as far away as the San Francisco Bay area, about 250 miles (400 km) south of Ferndale.

The Bay Area Rapid Transit agency said on Twitter it was running its system with a 10-minute delay and with trains traveling at reduced speeds due to the quake. The move was a standard precaution by BART.

Thirty minutes later, the transit agency tweeted that it was getting back on schedule.

"That was a big one," Twitter user Antonis Papatsaras of San Francisco wrote on the social media site in reference to the quake.

"Felt 20 seconds of very light shaking," tweeted another San Francisco resident, Lila LaHodd.

The quake was first reported with a 6.9 magnitude but downgraded by the USGS to 6.5.