A California hospital on Wednesday disclosed the birth of the world's smallest baby ever to survive, weighing a mere 245 grams (8.6 ounces) -- the same as a large apple -- when she was born.

The girl, nicknamed Saybie by hospital staff, was born 23 weeks and three days into her mother's pregnancy at Sharp Mary Birch Hospital for Women and Newborns in San Diego.

The father was told by doctors that he would have about an hour with his daughter before she passed away.

"But that hour turned into two hours which turned into a day, which turned into a week," the mother said in a video released by the hospital.

Doctors said Saybie was delivered via emergency cesarean section in December at 23 weeks and three days gestation in the womb after severe pregnancy complications that put her mother's life at risk. A typical pregnancy lasts 40 weeks.

After nearly five months at the hospital's neonatal intensive care unit, Saybie was discharged home earlier this month weighing a healthy five pounds (2.2 kilograms) and sporting a graduation cap.

"She is a miracle, that's for sure," said Kim Norby, one of the nurses who cared for Saybie as she fought to survive -- with a sign by her crib that read "tiny but mighty" cheering her on.

Emma Wiest, another nurse featured in the video, said Saybie was so small at birth that "you could barely see her on the bed." At birth, she weighed as much as a child's juice box or two sticks of butter and could fit in the palm of the hands of her caretakers. "I'd heard that we had such a tiny baby and it sounded unbelievable because I mean she's about half of the weight as a normal 23-weeker," Wiest said.

Doctors said that apart from Saybie's fighting spirit, her survival as a micro preemie -- a baby born before 28 weeks' gestation -- could be attributed to the fact that she suffered no serious complications after birth.

"Saybie experienced virtually none of the medical challenges typically associated with micro preemies, which can include brain bleeds, and lung and heart issues," the hospital said.

Saybie's ranking as the world's tiniest baby ever to survive is according to the Tiniest Babies Registry, maintained by the University of Iowa.

The previous record was held by a baby born in Germany in 2015 who weighed seven grams more than Saybie.

"Every life is a miracle -- those that defy the odds even more so," Edward Bell, a professor of pediatrics at the University of Iowa who oversees the registry, told AFP. In the video released by the hospital, Saybie's mother said the birth was the scariest day of her life.

She said she was rushed to hospital after feeling ill and was told she had preeclampsia -- a condition marked by very high blood pressure that puts both the mother and baby's lives at risk.

"They had to deliver her really quickly and I kept telling them that she's not going to survive, she's only 23 weeks," the mother, who did not want to be identified, said. But against all odds, Saybie did survive.

She nonetheless will still face enormous challenges as a micro-preemie, including possible respiratory, hearing and vision problems.