The patrol boats were sent to assert China's sovereignty over the islands known as Diaoyu in China and Senkaku in Japan, China's official New China News Agency reported.
State media said China's coast guard had "drafted an action plan for safeguarding the sovereignty and would take actions pending developments.
The dispatching of Chinese ships is certain to heighten tensions between the two countries, the Los Angeles Times reported.
Last month activists from both countries landed on one of the uninhabited islands to assert their country's sovereignty.
Japan's announcement Monday that it had made a deal to buy the islands southwest of Okinawa for $26 million produced a strong rebuke from China.
The uninhabited islands, believed to be rich in natural resources, have been under Japanese control but are also claimed by China and Taiwan.
Taiwan's foreign ministry recalled it's representative to Japan Tuesday to protest the Japanese action.
Foreign Minister Timothy Yang told a news conference the government had filed a strong protest against Japan's move, CNA, the central news agency, reported.
Japan's cabinet was expected to sign the island sale contract Tuesday, Kyodo News reported.
In a lengthy statement, the Chinese Foreign Ministry said the "nationalization" of the islands is "totally illegal and invalid" and constitutes "a gross violation of China's sovereignty over its own territory and is highly offensive to the 1.3 billion Chinese people ... . The Chinese government and people express firm opposition to and strong protest against the Japanese move."
The statement said the islands have been China's "sacred territory since ancient times."
"The Diaoyu Islands have been put under the jurisdiction of China's naval defense as affiliated islands of Taiwan, China, since the Ming Dynasty," the statement said, adding Japan "illegally occupied" the islands in 1895 when the Qing government's defeat in the First Sino-Japanese War was almost certain.
The Foreign Ministry said in recent years Japan has "repeatedly stirred up troubles" over the islands and its government has endorsed "right-wing forces to clamor" for the purchase of the islands and pave the way for their government control. The statement said the purchase of the islands runs counter to the "goal of upholding the larger interest of China-Japan relations."
The statement warned: "Long gone are the days when the Chinese nation was subject to bullying and humiliation from others. The Chinese government will not sit idly by watching its territorial sovereignty being infringed upon. ... Should the Japanese side insist on going its own way, it shall have to bear all serious consequences arising there from."