China's official Xinhua News Agency reported that the China Marine Surveillance ships had reached waters off the disputed islands on Tuesday. The ships, which are often lightly armed, are prepared to "take actions pending the development of the situation," the news agency said.
China is seeking to protect its sovereignty over the island in the face of Japan's latest bid to assert its control in the area.
On Monday the Japanese government announced that it had completed its planned purchase of the islands, which are claimed by both nations. Known to Japanese as the Senkakus and to Chinese as the Diaoyus, the islands lie in a strategically important shipping region, believed to be rich in valuable mineral resources.
Japan, which already controls the islands, said it doesn't expect the purchase to stoke long standing tensions.
"This should cause no problem for Japan's ties with other countries and regions," said Japan's Chief Cabinet Secretary Osamu Fujimura said on Monday.
"We have absolutely no desire for any repercussions as far as Japan-China relations are concerned. It is important that we avoid misunderstanding and unforeseen problems," he told reporters.
But ahead of the deal Beijing warned that Japan would suffer unspecified consequences if it went ahead with the purchase from private owners.
Chinese Premier Wen Jiabao has described the islands as "an inherent part of China's territory." He has vowed his country would "never ever yield an inch" on its sovereignty.
ccp/sej (AP, AFP)