SAN DIEGO, April 6 (Xinhua) -- San Diego Zoo in U.S. state of California held a special ceremony on Saturday to kick off a three-week farewell celebration for two giant pandas.

Twenty-seven-year-old female giant panda Bai Yun and her son, 6-year-old Xiao Liwu will leave the San Diego Zoo in late April and be sent back to China, as the Zoo's conservation loan agreement with China has ended.

According to the zoo, their staff are working with their colleagues in China on the future of panda conservation and research.

The San Diego Zoo giant panda program is the first joint research program established between China and the United States as early as in 1994, said Zhang Ping, Chinese Consul General in Los Angeles.

"Like other joint giant panda research and conservation programs in the United States, this program has not only promoted the friendship and understanding between the Chinese and American people, but also pushed forward the bilateral collaboration and joint research on protection and conservation of endangered species of wildlife and biodiversity," he said.

Erica Kohler, director of operations of the San Diego Zoo, told Xinhua it is sad to see the two pandas leaving for China. However, it is also a time for celebrating the successful collaboration with China on joint research of panda breeding and wild life protection.

Calling panda a friendship ambassador from China, she said Bai Yun and Xiao Liwu attracted about two million visitors to the San Diego Zoo each year.

As the first panda on loan, Bai Yun, arrived at the San Diego Zoo in 1996 from China. The cuddly panda soon became an iconic image of the zoo and one of the most popular animals. The name of her son, Xiao Liwu, means Little Gift in English.

The farewell celebration will last until April 27 for visitors to bid farewell to the two pandas.