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Video of a live whale shark being sawed on a fishing quay in southern China, its mouth agape and moving and blood gushing out as workers sliced it to pieces, has startled and repelled viewers.

CCTV, the Chinese state broadcaster, reported on Tuesday that a local fisheries department in Yangjiang, in Guangdong Province, was investigating the case.

“The whale shark is a second-grade protected animal in China,” the report said. “Killing protected animals in China is a crime.”

The whale shark, the world’s largest fish, can grow to about 10 meters, or more than 30 feet, long, and it can weigh as much as 9 metric tons, or 20,000 pounds. It is also protected internationally, classified as an Appendix II animal by the Convention on International Trade in Endangered Species of Wild Flora and Fauna, meaning that trade in the fish is controlled “in order to avoid utilization incompatible with their survival.”

Revulsion at the sawing, video of which began circulating Thursday, has prompted many online comments, China Daily reported.

“Many online friends are passing this clip around and calling it cruel, saying, ‘The live sawing of the whale shark is very inhumane,’ ” the newspaper quoted one commenter as saying. “The video is heartbreaking and difficult to watch,” read another comment it cited.

“Imagine, after it was caught they didn’t knock it out, but cut up, bit by bit they cut it up — that’s so cruel,” a commenter called Duo Mu wrote on hainan.net.

Chinese fishermen and fish factory workers are believed to kill and process many hundreds, probably thousands, of whale sharks each year, according to animal welfare advocates. The species feeds on plankton and is thought to pose little threat to humans.

In a report published last year titled “Planet’s biggest slaughter of whale sharks exposed in Pu Qi, Zhejiang Province, China,” Alex Hofford and Paul Hilton of WildLifeRisk, a conservation organization, wrote that a single whale shark could sell for around $31,000.

The trade, which they said was illegal, was producing “a lot of carnage” and “a lot of damage,” Mr. Hilton said in an interview last year. Shark parts were being sold internationally for meat as well as for oil for the cosmetic and pharmaceutical industries, Mr. Hofford and Mr. Hilton said.

Follow Didi Kirsten Tatlow on Twitter @dktatlow.