U.S.-born panda Bao Bao celebrated her fourth birthday in southwest China's Sichuan Province Wednesday.

Staff with the Dujiangyan base of the China Conservation and Research Center for Giant Panda prepared a 50-kilogram birthday cake made from bamboo, carrots, steamed buns and apples.

Bao Bao (Treasure) was born on Aug. 23, 2013 at the Smithsonian's National Zoo in Washington D.C., the second panda born there.

Her parents Mei Xiang and Tian Tian moved to the American zoo in 2000 under a cooperation agreement between China and the United States. According to the agreement, panda cubs born in the United States to parents on loan from China must be returned to China so that they can enter breeding programs.

Bao Bao arrived in Chengdu on Feb. 22 this year before being quarantined for a month.

More than 100 tourists and staff gathered for Bao Bao's birthday party. American tourist Charlin, who watched the live transmission of Bao Bao's birth four years ago, traveled to Sichuan from Virginia to attend the party.

"I hope she is healthy and happy here," she said.

Bao Bao's carer Zou Wenyong said that when Bao Bao first returned to China, she was still living on American time and was excited late at night and early morning.

"She liked biscuits from the United States and was insensitive to my instructions when she returned. After six months of training, she is accustomed to life here," Zou said.

"At the beginning, Bao Bao wouldn't eat steamed buns, so I had to cut the buns into thin slices and dip them into honey, a lot of honey. I had to get her used to the Chinese diet," he said. "Then I started to cut the buns into bigger chunks and reduce the amount of honey. Now she can eat 1,200 grams a day."

The panda has put on eight kilograms since her return.

The panda breeding center has similar collaborations with 12 zoos in 10 countries.