A 6.4-magnitude earthquake shook Humboldt County in Northern California early Tuesday morning, the United States Geological Survey reported, leaving tens of thousands of customers without power.

The extent of damage or injuries had not been fully assessed after the quake struck, at 2:34 a.m. local time, about 12 miles west of Ferndale. By 5 a.m., poweroutage.us reported that about 72,000 customers in Humboldt County, about 72 percent of the total customers there, were without power. The oceanside county is more than 200 miles north of San Francisco.

The Humboldt County Sheriff’s Office said on social media that “widespread damages to roads and homes are reported throughout Humboldt County,” and encouraged residents to check gas and water lines for damage or leaks. It asked people to avoid calling 911 unless they were experiencing an immediate emergency.

There were more than two dozen aftershocks by 4 a.m., including at least five that were magnitude 3 or higher, the U.S.G.S. reported.

One of the roads damaged was near the Fernbridge, a historic bridge that crosses the Eel River and serves as the primary route for Ferndale residents to reach Eureka, the county’s largest city. The bridge was closed early Tuesday, and photos showed that a billowing crack had formed in the nearby road.

Shane Wilson, chief of the Rio Dell Volunteer Fire Department, said Tuesday morning that two structure fires were reported, both causing minor damage. But there was “significant structure damage,” including houses separated from foundations, he said.

All of the injuries reported in Rio Dell were minor, he said.

In Rio Dell, Joe Filyau, 59, said that he had been through other earthquakes, but “never felt one that hard.”

The “earth was just slamming up and down,” he said. A tile from the countertop in his newly renovated kitchen broke away from the wall, and he had to turn the water off after a line burst, spraying water under his house.

“Everything in the house is just everywhere,” he said.

But Mr. Filyau had more pressing concerns: His 87-year-old mother, Beverly, is on oxygen, and he did not know how much longer their gas-powered generator would last. All of the nearby gas stations were closed, and he planned to drive to Ferndale, hoping that a gas station there would have power.

Caroline Titus, a journalist in Ferndale, posted a photo on Twitter showing items in her home spread across the floor after apparently falling off a shelf. “House is a mess,” she said.

The earthquake came exactly one year after a 6.2-magnitude quake struck in nearby Cape Mendocino, also in Humboldt County.

The National Tsunami Warning Center said no tsunami was expected.

NYTNS