Buildings are damaged and tens of thousands of people are without power after a large earthquake shook California’s North Bay area Sunday morning.

The U.S. Geological Survey has dubbed the seismic event the "South Napa earthquake" and say it is the largest quake to hit the region in almost 25 years.

In the hours since the quake struck, the geological survey group has published detailed information about the size and reach of the event. Here are five things to know about the South Napa earthquake:

1. The South Napa earthquake’s epicentre was approximately 9 kilometres southwest of Napa, Calif., a town of about 77,000 people. The epicentre was only 6 km northwest from American Canyon, a town of 19,000. The effects were also felt in San Francisco, Sacramento, and Oakland, where the survey group classified the shaking as "light."

2. The earthquake hit at 3:20 a.m. local time, sending some residents fleeing their homes while others slept.

3. The quake had a magnitude of 6.0. That makes it the largest earthquake in the area since the 6.9 magnitude Loma Prieta earthquake in 1989, according to the U.S. Geological Survey.

4. The U.S. Geological Survey website says the likelihood of casualties is very low. Approximately 15,000 people are estimated to have felt “severe” shaking, while 177,000 would have felt "very strong" shaking. In total, 1.5 million people are estimated to have felt "weak" shaking, the organization’s website says. The USGS estimates "moderate" economic damage between $100 million and $1 billion.

5. The earthquake occurred in the San Andreas Fault system, on the borders of the Pacific and North American tectonic plates.

The epicentre was located between two major strike-slip fault systems. The Hayward Rodgers Creek Fault system is about 7 km west of the quake site and the Concord-Green Valley Fault system is 12 km east. Both fault systems have generated major earthquakes in the past.

The U.S. Geological Survey is crowdsourcing more data on the quake to get a better understanding of what happened. If you felt the South Napa earthquake, the organization asks you to tell them about it online.