Scientists have carried out the first successful in vitro fertilisation of a southern white rhino, a major breakthrough that could pave the way to saving its highly endangered northern cousin.

Only two female northern white rhinos remain in existence but neither is capable of carrying a pregnancy to term.

To save the functionally extinct species, researchers from the scientific consortium Biorescue are attempting to implant a lab-grown northern white rhino embryo in a southern surrogate.

The ambitious reproduction programme is the last chance at survival for the northern white rhino species, whose last two members live at the Ol Pejeta Conservancy in Kenya under 24-hour guard to protect them from poachers.

The successful impregnation of a southern white rhino with an embryo of the same species was a "milestone", project leader Thomas Hildebrandt said at a press conference in Berlin.

"We achieved something that was not believed to be possible," Hildebrandt said.

The successful recent trial ended in tragedy when the bull and the surrogate, along with the foetus, were killed by an unrelated infection the scientists believe was caused by bacteria released by a mudslide in their enclosure.

The foetus was only 70 days old at the time but the team said they were confident it could have survived the 16-month pregnancy period.

The next step will see scientists try to repeat the feat with other embryos made with eggs harvested from the surviving females and sperm preserved from two long-dead males.

The team aims to "produce northern white rhino calves in the next two to two-and-a-half years," Hildebrandt said. (AFP)