Images of skeletal sun bears in a zoo in Indonesia that show the animals being forced to eat their own faeces and begging visitors for food have sparked online petitions to save them, media reports say.

A video taken by animal welfare group Scorpion at Bandung zoo on the island of Java showed one emaciated animal in a small dirty pen, reported 9news.com.au.

The footage, reportedly shot earlier this month, showed how one of the sun bears had become so desperate for food that it ate its own faeces.

It also showed visitors hurling cake, sweets and snacks at the bears in a desperate attempt to feed them, according to The Sun.

Volunteers from Scorpion said the sun bears in the zoo were only a fraction of their healthy 80kg weight.

According to media reports, the volunteers had asked zoo officials for permission to visit and inspect the animals but said they were refused access.

The group has started an online petition calling on the local mayor to close the zoo. The petition has since gathered 1,500 signatures.

Gunung Gea, the director of Scorpion, told Daily Mail Australia: "When my team visited the zoo last week there was no grass or live trees on the floor of their cage.

"We saw a sun bear eating its own dung but when we contacted the zoo's officers they told us the bear was medicated and we weren't allowed to see it."

Animal activist Tori Hollingsworth was so outraged by the video that she decided to create her own petition - which has 12,000 signatures so far - demanding the zoo be shut.

"The bears are extremely thin and very hungry. Appalled visitors give them junk food to try and keep them alive," she was quoted as saying by Daily Mail.

"It is obvious that this zoo is not helping the animals. It is nothing short of a prison."