An aerial view of Qilianyu islands in the Paracel chain, which China considers part of Hainan province on August 10, 2018. (Photo by AFP) / China OUT / CHINA OUT 

HANOI, Vietnam - Ten Vietnamese fishers were violently robbed in the disputed South China Sea, state media reported Wednesday, with an official saying the attackers came from Chinese-flagged vessels.

The men were reportedly beaten with iron bars and robbed of thousands of dollars worth of fish and equipment on Sunday off the Paracel Islands -- an archipelago in the resource-rich waterway claimed by China, Vietnam, the Philippines, Taiwan, Malaysia and Brunei.

Vietnamese media did not identify the nationalities of the attackers, but Phung Ba Vuong, an official in central Quang Ngai province told AFP: "They were Chinese, (the boats had) Chinese flags".

Four of the 10-man Vietnamese crew were rushed to hospital on Monday after arriving at Quang Ngai port, according to state-run Tien Phong newspaper, which said the men were attacked by around 40 people for three hours.

"Wearing chequered clothes, they cruelly beat us with iron bars," Captain Nguyen Thanh Bien was quoted as saying, adding that he fell unconscious for around an hour after the attack.

Footage on Tien Phong's website showed the fishers being taken from their boat on stretchers. One had a broken leg and two suffered broken arms, the report said.

Captain Bien told authorities that around $20,000 worth of equipment and fish had been stolen in the attack.

Party official Vuong -- who chairs the people's committee of Binh Chau, the commune where the fishermen live -- said on Facebook he "strongly opposed the barbarous acts by China."

Neither the foreign affairs ministries of Vietnam nor China immediately replied to a request for comment from AFP.

In a separate incident on Sunday, Tien Phong newspaper said another Vietnamese fishing boat in the Paracels was robbed of up to $12,200 worth of equipment and fish.

Beijing claims almost the entirety of the South China Sea, a waterway of immense strategic importance through which trillions of dollars of trade transits every year.

There are rival claims to parts of the sea from neighboring countries, including Vietnam, but China has become increasingly aggressive in asserting itself in the area.

The incident comes several weeks after Chinese army Lieutenant General He Lei said China "will resolutely crush any foreign hostile encroachment on China's territorial, sovereign and maritime rights and interests".

He made the statement on the sidelines of a defense forum in Beijing following a series of high-profile confrontations with Philippine ships in the waters.