News photos showed dozens of people smiling and clapping behind a waist-high fence as two men lifted the door of a small cage with metal bars and the panda wandered out. Police with riot gear stood guard, "in case it ran wild," Xinhua said.
"When the door of its cage opened ... Xiang Xiang hesitated for a second, then walked slowly for a few steps and eventually ran into a bamboo forest" about 30 feet away, Xinhua said.
It is the first time a panda raised in captivity has been released in China, Xinhua said. Xiang Xiang will be tracked by a global positioning device attached to his collar.
The 176-pound bear was chosen because he is "very strong and healthy," Xinhua said. He has been given a number of inoculations and a full physical checkup, it said.
Employees who answered the telephone at the Wolong center on Friday all said they were too busy or did not have permission to answer questions from reporters.
Xiang Xiang, whose name means auspicious, has learned how to build a den, forage for food and mark his territory, experts at Wolong have said. He has also developed defensive skills like howling and biting.
His training began in 2003 in a 215,000-square-foot open-air facility and he was later transferred to an area 10 times the size to simulate a natural habitat.
Zhang Hemin, director of the Wolong center, said the bear was released now because his favorite food, bamboo shoots, are sprouting, making it easier for him to survive.
There are only about 1,600 wild pandas in the mountain forests of central China — the only place in the world they are found — and more than 180 live in captivity.
Pandas are threatened by loss of habitat, poaching and a low reproduction rate. Females in the wild typically have a cub once every two to three years.
Experts from the World Wildlife Fund have said that preserving panda habitats are critical for the animal's continued survival.
Xiang Xiang's release marks "a significant change" in the way the endangered species are saved, by training the pandas to live in the wild before releasing them, Zhao Xuemin, deputy head of China's State Forestry Administration, was cited as saying by Xinhua.
Liu Bin, 28, Xiang Xiang's keeper, said he had tears in his eyes while seeing the panda off.
"Xiang Xiang is just like my child who has grown up and will leave the family to live a life independently," Liu was quoted as saying. "I hate to part with Xiang Xiang but I hope it can survive on its own and will not forget me."