A species of rhino facing 'almost certain' extinction has new hope after a birth at a zoo in the US.

The San Diego Zoo has welcomed only the third-ever southern white rhino calf to be born through artificial insemination.

The zoo said the healthy male and mother are doing well after a 30-minute labour on Sunday and are now bonding in a "quiet nursing setting."

Artificial insemination has rarely been successful amongst the breed and the new calf is the first born through the technique in the US.

Although the southern white is classified as Near Threatened, its numbers have recovered over the past century - with around 18,000 now remaining in the wild.

A new-born southern white rhino calf at San Diego zoo is only the third in the world to be born through artificial insemination. Image: San Diego Zoo

Northern White Rhino

However, scientists now hope to use a similar technique to save the closely-related northern white species - which lost its last male in March 2018.

There are only two northern whites left, both of whom are female; however, conservationists hope to save the species by implanting sperm and embryo from a northern white into a southern white surrogate mother.

BIG NEWS: The pitter patter of little hooves at the Nikita Kahn Rhino Rescue Center ushered in a historic milestone yesterday as Victoria gave birth to a healthy male calf. ❤️ pic.twitter.com/vXn3hh1e6v

— San Diego Zoo Safari Park (@sdzsafaripark) July 29, 2019

"All of us at San Diego Zoo Global are elated with the arrival of this special rhino calf," said the zoo's  Director of Reproductive Sciences, Barbara Durrant.

"We are so pleased Victoria and the calf are doing well.

"She is very attentive to her baby, and the calf is up and walking, and nursing frequently.

"Not only are we thankful for a healthy calf but this birth is significant as it also represents a critical step in our effort to save the northern white rhino from the brink of extinction."

Brink of extinction

The last surviving members of the species – mother and daughter Najin and Fatu – live in Kenya's Ol Pejeta Conservancy.

Neither can bear offspring, leading many conservationists to warn their extinction was all but certain.

While scientists have preserved sperm samples from several male northern rhinos, they have yet to receive permission from the Kenyan Government to harvest eggs form the two females.

There are other options available if this does not happen.

Scientists have already implanted a hybrid rhino embryo into a southern white female; however, it is not clear whether the pregnancy will take.

Stem cells

Meanwhile, the San Diego Zoo said it aims to convert preserved cells from 12 northern males into stem cells that could develop into sperm and eggs.

Scientists will then consider different reproductive options including artificial insemination, IVF and embryo transfer working with southern whites.

"The reproductive system of rhinos is very complex, and there is still much to be learned," the zoo said in a statement.

"There are many challenges ahead, but researchers are optimistic that a northern white rhino calf could be born from these processes within 10 to 20 years."

The zoo said the techniques could potentially be applied to other rhino species, including critically endangered Sumatran and Javan rhinos.