EXCLUSIVE: Disturbing video emerged from China Tuesday showing donkeys being tortured -- some bashed in the head with sledgehammers -- for what has become a lucrative business: the slaughter of donkeys for a traditional Chinese medicine and a snack food product called ejiao.

The undercover video, obtained by People for the Ethical Treatment of Animals (PETA), shows donkeys as young as 5 months being killed so that their skins can be used to produce a brown gelatin, which is an essential ingredient in Chinese ejiao products.

The video, shot by workers from PETA's Asia division and released to Fox News, shows one donkey so malnourished that his ribs stick out and another hit in the forehead with a sledgehammer before having her throat slit. Some of the animals killed in this manner continue to breathe and move after being struck, according to the group.

GRAPHIC WARNING: Click here to view PETA's video

The animal rights group said the video shows one of the worst cases of animal brutality in the world.

"Donkeys as young as 5 months old have been bashed in the head and left to die a slow, agonizing death, all for an ingredient," PETA President Ingrid Newkirk said in a statement.

"PETA is calling on kind people in China and everywhere to choose only foods and medicines that do not contain donkey gelatin and to encourage their friends and family members to do the same," Newkirk said.

PETA's investigation lead them to farms in China, where the donkeys were confined to small, filthy concrete-floored pens and forced to stand in their own excrement. The only water available to them was filthy and green with algae.

PETA said its observers witnessed terrified animals beaten with sticks, including a donkey who was hit and screamed at when she attempted to escape through a gate that had been left open.

PETA said its observers witnessed terrified animals beaten with sticks, including a donkey who was hit and screamed at when she attempted to escape through a gate that had been left open.

The animal rights organization is calling for an international ban on the trade in donkey skins to produce ejiao products, popular in Chinese health foods and traditional medicines -- despite modern medical research minimizing its efficacy. A report by BBC News says that ejiao can sell for up to $388 per kilo.

There is an increasing demand for ejiao, which can also be found in some candies, snacks and beauty products available in the U.S. According to PETA, donkeys are now being imported into China for slaughter and horses, pigs and cows are being killed for fake ejiao to meet such a demand.