The mother, who was not identified, gave birth to six boys and two girls weighing between 1.8 pounds and 3.4 pounds, doctors at Kaiser Permanante Medical Center told The Associated Press.
"It's a surprise," Dr. Karen Maples said. "Eight newborns are in stable condition and they're doing quite well."
Kaiser spokeswoman Myra Suarez said she could not release any information about the mother, including her condition or whether she used fertility drugs. Such drugs make multiple births more likely.
"They are all doing the best they can," Suarez told the AP.
The first baby was born at 10:43 a.m.; the eighth one at 10:48 a.m.
"They were all screaming and kicking around very vigorously," Dr. Harold Henry told the TV station.
The first live-born octuplets were born in Houston in 1998, and one baby died about a week later. The surviving siblings — girls Ebuka, Gorom, Chidi, Chima and Echerem, and their brothers Ikem and Jioke — celebrated their 10th birthday in December.
Their parents, Nkem Chukwu and Iyke Louis Udobi, said they are astonished and grateful that their children have grown up to be healthy and active kids who are now in the fourth grade.
Chukwu said the new parents have much to look forward to.
"Just enjoy it. It's a blessing, truly a blessing," Chukwu said. "We'll keep praying for them."
The Bellflower medical center is about 17 miles southeast of Los Angeles.