Lifeguards pulled two unconscious young men from the water at Moonlight Beach in Encinitas on Thursday, the San Diego County Sheriff's Department said.
The two were then rushed to Scripps Memorial Hospital. Their conditions are unknown.
One appeared to be a minor, the other possibly in his late teens or early 20s, officials said.
Deputies walked the beach but could find no one who could identify the two, said Sheriff's Lt. Amy Brown-Lisk.
The incident occured during a strong rip current that required several rescues by lifeguards.
"It's been extremely dangerous these last few days," said Marlena Medford, spokeswoman for the city of Encinitas.