Officials from Taiwan's Coast Guard Administration said five patrol boats had been sent to protect a boat, the Chuan Chia Fu and the nine people on it, after it sailed into waters close to the Diaoyu Islands in the East China Sea, in a move to strengthen sovereignty over the islands.

Taiwan officials said that the boat left Taiwan at 11 pm on Tuesday and sailed into the waters 2.7 nautical miles from the Diaoyu Islands and left the area around 9 am Wednesday.

The Japan Coast Guard said a fishing boat carrying Taiwanese activists was spotted sailing Wednesday morning near the Diaoyu Islands in the East China Sea and "eventually entering Japanese territorial waters," the Kyoto News reported.

A Japanese coast guard aircraft spotted the boat about 37 kilometers southwest of the Diaoyu Islands.

Japanese Chief Cabinet Secretary Osamu Fujimura told a news conference Wednesday, "We do not know their objective but whatever the purpose, we will definitely not tolerate the action of entering (Japanese) waters."

A liaison team has been set up at the prime minister's office to maintain surveillance, the government's top spokesman said, according to the report.

The mainland has urged Japan not to take any action that could endanger Chinese lives and property following a Taiwanese vessel's entry into waters near the Diaoyu Islands, a foreign ministry spokesman said Wednesday.

"We have already urged the Japanese side to refrain from taking action that could endanger lives and property, including those of our Taiwanese compatriots," Liu Weimin said at a press conference.

The Diaoyu Islands and its affiliated islands have been China's inherent territory since ancient times and China has undisputable sovereignty over the islands, Liu said.

The mainland will continue to take necessary measures to firmly safeguard its sovereignty over the Diaoyu Islands, he said.

"These actions from Taiwan might deter Japan from coveting our territory, and it would also alleviate the relations across the Taiwan Straits, promoting cooperation between the mainland and Taiwan," Sun Yingchun, a professor at the Communication University of China, told the Global Times.

"Considering the fact that Russian Prime Minister Dmitry Medvedev on Tuesday made a repeat trip to one of the four Pacific Kuril islands, China should also ignore Japan's attitude when protecting our inherent territory," Sun said.

Japan's diplomatic incompetence should be blamed for the strained relationship with its neighboring countries when dealing with conflicts, Geng Xin, an international relations analyst said. "But Japan firmly believes that the capability of resolving territorial disputes is a main parameter for a major power. There is no quick solution to the issue."