A dead whale that washed ashore in eastern Indonesia had a large lump of plastic waste in its stomach, including drinking cups and flip-flops, a park official said Tuesday, causing concern among environmentalists and government officials in one of the world's largest plastic polluting countries.

Rescuers from Wakatobi National Park found the rotting carcass of the 9.5-metre-long sperm whale late Monday near the park in Southeast Sulawesi province after receiving a report from environmentalists that villagers had surrounded the dead whale and were beginning to butcher the remains, park chief Heri Santoso said.

Santoso said researchers from wildlife conservation group WWF and the park's conservation academy found about 5.9 kilograms of plastic waste in the animal's stomach containing 115 plastic cups, four plastic bottles, 25 plastic bags, 2 flip-flops, a nylon sack and more than 1,000 other assorted pieces of plastic.

"Although we have not been able to deduce the cause of death, the facts that we see are truly awful," said Dwi Suprapti, a marine species conservation co-ordinator at WWF Indonesia.

She said it was not possible to determine whether the plastic had caused the whale's death because of the animal's advanced state of decay.

Indonesia, an archipelago of 260 million people, is the world's second-largest plastic polluter after China, according to a study published in the journal Science in January. It produces 2.9 million tonnes of mismanaged plastic waste a year, of which 1.17 million tonnes ends up in the ocean, the study said.

Plastic waste found in the whale's stomach included drinking cups and flip-flops, a park official said Tuesday. (Muhammad Irpan Sejati Tassakka, AKKP Wakatobi via AP)

Luhut Binsar Pandjaitan, Indonesia's co-ordinating minister of maritime affairs, said the whale's discovery should raise public awareness about the need to reduce plastic use, and had spurred the government to take tougher measures to protect the ocean.

"I'm so sad to hear this," said Pandjaitan, who recently has campaigned for less use of plastic. "It is possible that many other marine animals are also contaminated with plastic waste, and this is very dangerous for our lives."

He said the government is making efforts to reduce the use of plastic, including urging shops not to provide plastic bags for customers and teaching about the problem in schools nationwide to meet a government target of reducing plastic use by 70 per cent by 2025.

"This big ambition can be achieved if people learn to understand that plastic waste is a common enemy," he told The Associated Press.