The hospital had scheduled a Caesarean section for seven babies, but doctors were surprised by the eighth.
"My eyes were wide," Dr. Karen Maples said, explaining her reaction to the last birth.
Doctors said the babies were born nine weeks premature but are in stable condition. Two newborns were placed on ventilators and a third needs oxygen.
Forty-six hospital staff and four delivery rooms were used for the births. After a baby was born, staff rushed the newborn into another room and waited for the next, the hospital said. But despite weeks of preparation, doctors did not expect the eighth child.
"It is quite easy to miss a baby when you're anticipating seven babies," said Dr. Harold Henry, chief of maternal and fetal medicine at the hospital. "Ultrasound doesn't show you everything."
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," Henry told KCAL9.
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 told the AP that the parents of the newest octuplets 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.
Associated Press writers Denise Petski and Alicia Chang in Los Angeles contributed to this report.
(This version CORRECTS full name of hospital.)