Anti-Japan protests across China intensified over the weekend as demonstrators vandalized Japanese products and businesses in more than fifty cities. With Japanese companies announcing plans to close temporarily, tensions between Asia’s two great powers mount.

The protests, coming after Japan purchased the disputed Senkaku Islands, known as Diaoyu in China, to which countries claim as sovereign territory, are believed to be the worst in years. Japan finalized a deal to purchase three of the islands from their private owner last week.

The move was likely taken to prevent tensions with China from escalating further after the outspoken governor of Tokyo, Shintaro Ishihara, said that he planned to buy them for development. However, when Prime Minister Yoshiko Noda took a hardline position when he reiterated that the islands are Japanese territory, both historically and from international law, nationalists in China were outraged.

China’s Foreign Ministry spokesman Hong Lei denounced the sale as illegal and said that China would take “necessary measures” to defend its sovereignty. Soon, two Chinese surveillance ships were seen around the islands, resulting in Japan mobilizing its Coast Guard. A few days later, six Chinese surveillance vessels were reported briefly entering Japanese waters. On Monday, a flotilla of up to 1,000 Chinese fishing boats was believed to be on their way to the islands.

American defense secretary Leon Panetta was in Japan over the weekend and announced an agreement to deploy a second radar on Japanese territory in order to beef up its missile defense systems. Panetta said that the system was meant as a defense to North Korean missiles but China believes that it is pointed against it.

Panetta arrived in Beijing on Monday and was scheduled to meet with Chinese vice president and leader in waiting Xi Jinping on Wednesday.

In the meantime, Japanese companies are halting business temporarily on the mainland as a result of the protests. Canon said that it would close its factories. Honda, Mazda and Nissan announced similar measures. Sony is said to be discouraging nonessential travel to China while popular Japanese retailer Uniqlo is closing stores too.

All sides are bracing for what happens on Tuesday, the anniversary of the Manchurian Incident of September 18, 1931. On that day, Japan staged an explosion on a Japanese owned railway which led to Imperial Japan’s invasion and occupation of China.

The protests may be orchestrated by the Chinese government as part of its longtime practice of whipping up nationalism, usually against Japan, to serve its geopolitical aims. Accordingly, the authorities allow Chinese nationalists to vent their anger for a period of time before putting an end to the unrest. By preventing the demonstrations from getting out of control, they allow the public to let off some steam and keep the protests from eventually threatening the Communist Party itself.

According to Caixan, a respected Chinese newspaper, the protesters are mainly males in their twenties and thirties. Its reporter approached one of the policemen guarding the protest route and asked if it was all right to take part without a permit, which the government requires. The policeman said that it was fine since “the organizer” had a permit. But when the reporter asked if it was okay to protest about corruption in China, the policeman said no. Only protests related to the Diaoyu Islands were permitted.