BEIJING - The relationship between China and Japan has been improving and it is time to foster more positive public opinions, Tokyo said.

The Japanese foreign ministry on Friday published its annual diplomatic blue book, which is a report on the country's foreign policy and activities.

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The latest report reviewed Tokyo's relationships with its neighboring countries in Asia. It said Sino-Japanese ties worsened after a boat collision in September 2010 but have now gradually stepped back on track toward improvement.

Last September, a Chinese fishing boat and a Japanese coast guard vessel collided near the Diaoyu Islands. Japan detained the Chinese captain for the incident.

After the devastating earthquake in northeastern Japan, the Chinese government quickly offered assistance, improving Sino-Japanese relations. Even little children living in China's remote areas donated to support disaster-stricken Japan.

"China's assistance to the Japanese quake victims this time will be a positive influence on the bilateral relationship with Tokyo. However, we cannot be overly optimistic," Gao Hong, an expert on Japanese studies from the Chinese Academy of Social Sciences, told China Daily.

He said that looking ahead, the relationship has to rely on a more comprehensive understanding of each other. "Excessive caution (against China) is a problem. In the past, China's economy was weak and Japan's was strong, and a certain balance was established. However, that situation no longer exists and in order to reach a new balance, both countries need to have more political trust and confidence to help increase mutual understanding," Gao said.

In the preface of the 2011 Bluebook, Japan's Foreign Minister Takeaki Matsumoto called the March 11 earthquake and tsunami as "the worst national crisis after World War II" and expressed the determination of the Japanese government to overcome this difficult time and achieve a revival.

Gao said the natural disasters, which subsequently induced a national nuclear crisis, could also influence Tokyo's future foreign policy. "International aid to Japan will be something that the government keeps in mind when dealing with other nations, but nonetheless its major policies will not change."

Reviewing its relationship with South Korea, which Japan said is its "most important neighbor", the diplomatic guidebook said the country will continue to strengthen relations between the two countries. Meanwhile, it repeated its territorial claims over South Korea's eastern islets of Dokdo, which Japan calls Takeshima.

South Korea's foreign ministry expressed regret and intends to protest Japan's stance. It plans to summon a diplomatic minister at the Japanese embassy in Seoul to file an official protest, according to Yonhap News Agency.

"Japan may soften its voice over some issues after the quake but that is never going to happen when it comes to territorial disputes. As a result, Tokyo's conflicts with Beijing and Seoul cannot be fundamentally resolved," said Zhou Yongsheng, a professor of Japanese studies at the China Foreign Affairs University.

Japan changes prime ministers and foreign ministers often, which is reflected in the Bluebook. According to the Asahi Shimbun, "The 2011 Bluebook reflects the political confusion since three foreign ministers and five deputy foreign ministers made their appearance."

For example, the East Asia Community (EAC) initiated by former prime minister Hatoyama disappeared in the newly issued report and more emphasis has been put on economic diplomacy promoted by Matsumoto's predecessor Seiji Maehara. It introduced Japan's new plan to expand abroad such as infrastructure projects and export of high-speed train technology.

"Having a revolving-door of leadership has long-term influence. To be specific, it easily weakens the consistency of a country's foreign policy," Professor Zhou said.