At the Spinning Wheel Diner in Lebanon, N.J., near the epicenter of the earthquake, the servers first heard the china loudly rattling on the metal kitchen shelves.

Some customers eating breakfast at the red vinyl booths darted out the double glass doors into the parking lot but found that outside was shaking just as badly as indoors, said Alexia Anastasiou, a hostess.

“The trees, the cars, the ground,” she said about an hour later. “Fifteen minutes after, I was still shaken up — I am still shook up.”

The people here did not know it yet, but the area — in the center of Hunterdon County, about 50 miles west of New York City and 60 miles north of Philadelphia — was the epicenter of the earthquake, according to the United States Geological Survey.

Some drivers said they were on the road and initially thought they were having car trouble; others said it felt like a bomb. At the diner, about an hour after the event, Terry DeRossett said he was at home in nearby Flemington, where the glass panes of his doors shook so hard he thought they would shatter.

“The house sounded like I was inside a drum,” he said. “It was like that feeling you get from a thunderclap, but it just kept going.”

At the Oldwick General Store in Oldwick, N.J., the quake was so loud that Kristina Feeley and her colleagues initially thought a truck had crashed into the building. Everyone froze, Ms. Feeley said, and it was several minutes before the floor felt steady enough to move across it.

“Everybody — customers too — are shaken up, getting up from their tables like, ‘Whoa, this is what it feels like to walk again.’”

The quake rattled the heart of the state’s horse country, an area where farm roads are lined with fields and stables.

Mane Stream, a therapeutic riding stable, is about 100 yards from where seismologists estimated the quake’s epicenter was. Trish Hegeman, the executive director, said she knew what was happening immediately, having lived in California for nearly a decade.

She ran to a door frame and braced herself for safety in the barn office. Minutes later she headed to the barn to check on the facility’s 13 therapy horses. All were calm.

“I think one whinnied,” she said. “Amazing, given that we are right at the center.”

At a riding stables in nearby Califon, the earthquake shook the indoor arena, causing an enormous booming sound that sent the three horses galloping around the ring, heedless of their riders’ efforts to stop them. As the shaking settled, the riders dismounted and tried to soothe their trembling horses.

Dr. Brendan Furlong, an equine veterinarian whose practice is nearby, said he was about to start a procedure on a horse under sedation in a concrete barn in Lebanon Township when the barn startled to rattle, items fell off shelves and the building started to squeak. The horse was jolted awake from the sedation, Dr. Furlong said.

“This poor horse,” he said, “he wanted to go somewhere.”

No one, including the horse, was injured.