Triplicate staff and The Associated Press

EUREKA Tremors from a 5.4-magnitude earthquake Monday morning off the coast hit Humboldt County, but authorities said there were no immediate reports of injuries or damage.

The U.S. Geological Survey said the moderate quake at 4:20 a.m. struck about 30 miles off the coast south of Eureka.

A Humboldt County Sheriff's Department dispatcher said the quake was felt at Eureka headquarters, but no one reported damage or injuries.

Other Eureka buildings, such as the three-story St. Joseph's Hospital, swayed during the quake, but were distant enough that nothing fell off shelves or walls. A number of patients simply slept through the quake, hospital officials said.

Earthquakes are not uncommon in Northern California, the USGS said.