Millions of Chinese people have a watched a US zoo say goodbye to a giant panda ahead of her much-discussed return home after 20 years.

A farewell party for 22-year-old Ya Ya at Memphis Zoo took place on Saturday.

She and her male mate Le Le, who died in February, had been monitored closely by Chinese people, after questions were raised over their treatment at the zoo.

It has previously denied such allegations and accused activists of spreading false information.

The zoo says Ya Ya has a chronic skin and fur condition, which "occasionally make her hair look thin and patchy".

Around 500 people attended the event in the Tennessee city, which featured Chinese cultural performances and goodbye letters.

Ya Ya was surrounded by bamboo and given a special ice cake made of grapes, sugar cane, and cookies, according to pictures and videos shared online. Many Chinese followed it live online.

"Safe travels Ya Ya. You will be missed by so many," a comment on the zoo's Facebook page read. "We will miss you... You have brought us so much joy," added a user on its Twitter page.

But other comments aimed at the zoo appeared more aggressive. "Stop faking your affection, you make me sick," said one comment in Chinese.

"Ya Ya [has] suffered such a hard time. Come back home - we're all waiting for you," another person wrote.

Ya Ya and Le Le arrived in the Tennessee city in 2003 on loan. China has long used so-called panda diplomacy to help foster relationships with other countries.

But in recent times, Memphis Zoo has been grilled by Chinese netizens over accusations that Ya Ya and Le Le had been mistreated during their stay.

It followed allegations - rejected by the zoo - that the pair had suffered physical and mental diseases.

A video posted by animal advocacy groups In Defense of Animals and Panda Voices last year showed the pandas pacing in circles. The groups said the animals appeared to have lost fur and weight, and called for them to be "returned to China before it's too late".

Zoo officials countered that they were "two of the most spoiled animals on the planet", according to Associated Press.

On its website, the zoo says: "Ya Ya lives with a chronic skin and fur condition. This condition does not affect her quality of life but does occasionally make her hair look thin and patchy. The condition is closely monitored by our animal care team and veterinary staff."