A woman in California has given birth to eight babies, six boys and two girls, becoming only the second person in the US medical history to have delivered a set of living octuplets.

The babies, who weighed between 0.69 kg and 1.47 kg, were delivered by caesarean section at Kaiser Permanente hospital in Bellflower, 30 km south of Los Angeles, yesterday.

The “very vigorous” babies, born in the space of five minutes, were nine weeks premature and all of them were generally doing well in incubators, doctors said.

The doctors and the mother, who requested anonymity, had expected seven babies, but were surprised when an eighth came out.

“After we got to Baby G, which is what we expected, we were surprised by Baby H,” Karen Maples, the chief of the hospital’s obstetrics and gynaecology department, said.

The first live-born set of octuplets in the US was delivered in Houston, Texas, in 1998. One baby died about a week later, but the surviving children celebrated their 10th birthday in December.

About the infants born yesterday, Harold Henry, the hospital’s chief of foetal medicine, said getting the number correct with ultrasounds before delivery is difficult with so many babies. “It is quite easy to miss a baby when you’re expecting seven,” Henry was quoted as saying by CNN.

Three of the babies needed breathing assistance, but otherwise none of them appeared to have serious problems, doctors said. “It was a truly amazing delivery,” Maples was quoted as saying.

The woman was 23 weeks pregnant when she was hospitalised seven weeks ago. Before the deliveries, a team of 46 physicians, nurses and other staff prepared for the births.

The hospital said it would not answer questions about whether the woman had fertility treatments.

The first three to seven days would be critical for the California babies, Mandhir Gupta, one of the doctors at the news conference, said, adding the infants could be in incubators for six to eight weeks and in the hospital for 10 weeks.