The police warning came after video clips posted online showed protesters, who believe the US was behind the ruling, demonstrating outside restaurants owned by the US fast-food chain KFC in cities such as Hebei, Jiangsu, Shandong and Hunan, state-run China Daily reported.
Several demonstrators held red banners saying "Join the boycott against US, Japanese and Philippine companies, and be a patriotic Chinese" and stopped people from entering the restaurants.
In recent years the ruling Communist Party of China has encouraged people to stage protests against Japan over the dispute over the islands in East China Sea.
Police have strengthened security at the Philippines embassy in Beijing after the tribunal on July 12 upheld the Philippines rights over the South China Sea.
Also Read
China has rejected the verdict and said it will not have any impact on its stand that over 90 per cent of the South China Sea belonged to it.
A KFC employee surnamed Lei in Chenzhou, Hunan province, confirmed there had been a small protest outside the restaurant on Monday. She said that business returned to normal today, China Daily reported.
Yum! Brands Inc, China Division, which operates the KFC chain in the country, declined to comment on the protests. The protests have been criticised by the police and public.
After one such protest was held at a local KFC, police in Ganyu district, Lianyungang, Jiangsu province, issued a statement yesterday urging people to not get involved in illegal protests instigated via the internet or social media.
In Siyang county, Jiangsu, police posted on their micro blog the message, "Love your country, but please don't take out your anger on its people."
"They are simply creating chaos in the name of patriotism. If KFC closes down, it's the locals who will be out of jobs," she said.