The cubs were born to mom "Mei Mei," who traveled to Japan from Chengdu Research Base of Giant Panda Breeding.

"The twin cubs, born in Adventure World in Wakayama, Japan, weighed 196 grams and 86 grams," said Zhang Zhihe, an expert with the base. "This is the sixth delivery of the 12-year-old mother, and she and the babies are all healthy."

Despite the early deaths of three cubs, this represents the biggest baby boom for the endangered species since China's first attempt to artificially breed giant pandas in the 1960s, he said.

Twenty-six of the surviving panda cubs were bred by zoologists in Southwest China's Sichuan Province: 17 were born at the Wolong Giant Panda Protection and Research Center and nine at the Chengdu Research Base. One of the twin pandas born in neighboring Chongqing Municipality also survived, and another was born at the Atlanta Zoo in the United States.

He said, "The record number of cubs this year shows the captive breeding of giant pandas has entered a golden age."