A swarm is a group of quakes, dozens to thousands, where there are many earthquakes close in size and no obvious mainshock.
Since Saturday morning, more than 350 minor quakes have hit near the city of Brawley, between the Salton Sea and the U.S.-Mexico border, according to the Southern California Seismic Network.
The strongest of them was a 4.7-magnitude quake that struck just after midnight.
Foreshocks started around 3 a.m. on Saturday.
The California Governor's Office of Emergency Services says it has been keeping an eye on the situation. So far, no major damage or injuries have been reported.
Earthquake expert Dr. Lucy Jones says this kind of activity is common for the Brawley Seismic Zone.
The city of Brawley stated on Sunday, saying it is continuing to monitor the earthquake activity in the region. Officials noted that crews have responded to several minor issues, including water leaks and utility concerns.
"At this time, there is no immediate threat to public safety and no major infrastructure damage has been identified within the city," the city wrote.
A viewer who didn't want to be shown on camera called the local ABC station on Saturday about the swarm and said she felt another earthquake while she was on the phone.
"I was just scared. All of a sudden, it was a big jolt, and everything started moving. I was like, 'Holy crud.' They just kept on coming and coming and coming and coming. And as we're speaking right now, I do feel it rumbling beneath me." Kathleen Singh said.
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