HONG KONG (AFP) - A set of panda triplets, the world's only known surviving trio, celebrated reaching their 100-day milestone in a Chinese zoo Wednesday as the public were allowed to visit them for the first time.

Their births at the end of July were hailed as a "miracle", given the animal's famously low reproductive rate, and fears that they may not survive have been quelled.

A video from Guangzhou's Chimelong Safari Park showed the three cubs sprawled on their fronts on a blanket in a small enclosure, nudging each other with their snouts and lying back yawning.

The two male and one female cubs, which first opened their eyes in September, now weigh six kilograms (13 pounds) each, the zoo said.

Visitors to their glass enclosure will be limited to 1,000 a day.

The celebration video traced the triplets' lives so far and portrayed the two young male cubs as looking up to their sister.

"Our older sister 'Long Long' leads us, and we are happy," the birthday song said.

The animals have not yet been officially named but will be soon, according to the zoo.

Their mother Juxiao, meaning "chrysanthemum smile", delivered the triplets at the zoo in the early hours of July 29.

The first known case of giant panda triplets was recorded in 1999, when a 15-year-old mother gave birth following artificial insemination in the southwestern Chinese city of Chengdu.

However the youngest of the trio died after living for just three days because of a bladder disorder.

Pandas, whose natural habitat lies in mountainous southwestern China, have a notoriously low reproductive rate and are under pressure from factors such as habitat loss. China has about 1,600 pandas living in the wild.