A baby gorilla has been delivered by a rare caesarean section at a British zoo in an operation performed by a hospital gynaecologist, the zoo said on Tuesday.

Vets at Bristol zoo in western England called in expert medical help after the mother Kera showed signs of potentially life-threatening pre-eclampsia.

Professor David Cahill, a gynaecologist at a nearby hospital who has delivered hundreds of babies by caesarean but never a gorilla, was drafted in to perform the operation, one of just a handful ever carried out worldwide.

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"Along with having my own children, this is probably one of the biggest achievements of my life and something I will certainly never forget," he said in a statement. "I have since been back to visit Kera and the baby gorilla, it was wonderful to see them both doing so well."

The baby girl gorilla weighed just over a kilogram (2 lbs 10oz) at birth 11 days ago. She initially needed help from vets to breathe independently but is now doing well after being hand-reared around the clock by keepers, the zoo said.

"The birth of any gorilla is a rare and exciting event; but the birth of a baby gorilla by caesareansection is even more unusual," said John Partridge, the zoo's senior curator of animals.

"It wasn't a decision that we took lightly – Kera was becoming quite poorly and we needed to act fast in order to give the best possible treatment to mother and baby, and to avoid the possibility of losing the baby."