Zoo keeper pets one of the white rhinos at the San Diego Zoo Safari Park. Photo: IC

A southern white rhino conceived through artificial insemination was born at the San Diego Zoo in what was called a historic milestone that could help save a subspecies from extinction.

The calf was born on Sunday and the mother named Victoria remained calm during the 30-minute labor, zoo officials said in a statement.

"We are so pleased Victoria and the calf are doing well," said Barbara Durrant, the director of Reproductive Sciences at the zoo. "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."

The birth marks the first successful artificial insemination birth of a southern white rhino in North America.

Victoria was inseminated with frozen semen from a southern white rhino named Maoto in March of 2018 and carried her calf for 493 days.

The successful birth has raised hopes that artificial insemination could help efforts to genetically recover the northern white rhino, a distant subspecies of the southern white rhino.

Only two northern white rhinos remain on Earth and both are female. The last male died in 2018.

There are an estimated 18,000 southern wild rhinos remaining in the wild but the species is also being decimated by poachers in South Africa at a rate of one every eight hours.

The San Diego zoo currently has six female southern white rhinos, which were relocated to the zoo's Safari Park from private reserves in Southern Africa in 2015.

Scientists hope the animals could potentially serve as future surrogate mothers for a northern white rhino. 

"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," zoo officials said.

As to Victoria and her calf, they will remain off-limits to visitors for the time being to allow them to bond.

And the newborn can expect a playmate in the near future as another rhino impregnated through artificial insemination is due to give birth in September or October.