A zoo has unveiled newborn giant panda triplets billed as the world's first known surviving trio in what is being hailed as a "miracle" given the animal's low reproductive rate.

It took almost four hours for the mother, Juxiao, to deliver the cubs, which weighed 83 grams, 90 grams and 122 grams, at Guangzhou's Chimelong Safari Park, Guangdong province, on July 29.

The triplets were put into incubators while Juxiao, meaning "chrysanthemum smile", regained her strength. They are now back with their mother who is nursing them under the watchful eyes of a team of zoo staff that looks after them 24 hours a day.