Three men have been detained for organizing protests to impede the operations of US fast-food chain KFC in Henan province, police said.

The men "illegally organized netizens to block two KFC restaurants" on Tuesday, according to the Puyang police micro blog.

The post said a man surnamed Li was placed under administrative detention for 15 days, while the other two, surnamed Yuan and Liu, were detained for 13 days each.

The incident was apparently triggered after a tribunal appointed by the Permanent Court of Arbitration in The Hague ruled in favor of the Philippines in a case against China over the South China Sea.

Photos showing people holding red banners reading "Boycott United States, Japanese and Philippine products", "Refuse the foreign rubbish food", and "Be a patriotic Chinese" outside a KFC were also posted with the announcement of the punishment.

In an earlier post on Tuesday, the Puyang police said they had noticed posts on messaging app WeChat inciting people to demonstrate against and boycott KFC. The post warned that anyone disturbing a company's production and operations would be punished under Chinese law.

"It's laudable for people to show patriotism, but it must be done without breaching the law," the post said.

Li Junfu, associate professor of sociology at Beijing University of Technology, said the punishment for the three is "appropriate" as their behavior resulted in losses to the two KFC restaurants' legal operations, and the punishments could warn others not to take similar actions.

He also said that people with poor education and limited sources of information are more likely to resort to such extreme behaviors.

There have been sporadic protests against the United States across China following the ruling.

Video clips posted online since Monday showed protesters who believe the US was behind the ruling demonstrating outside KFC restaurants in Hebei, Jiangsu, Shandong and Hunan provinces.