The Diaoyu Islands saga shows that Hong Kong has a role to play in China's diplomacy and handling of regional territorial disputes in the East China Sea, analysts say.
They say that Hong Kong activists' trip to the disputed islands this week supports Beijing's claim of sovereignty, while avoiding direct confrontation with Tokyo.
China's stance on the Diaoyus, which Japan calls the Senkaku Islands, has led to heated exchanges; Beijing responded furiously to Japanese Prime Minister Yoshihiko Noda's recent comments that Japan might buy the islands from their private Japanese owners.
Nevertheless, activists on the mainland have been barred from taking strong action.
"Given that the previous plans by Hong Kong activists to sail to the Diaoyu Islands were blocked by the authorities, it is fair to say that their recent successful attempt has been approved by Beijing," said Professor Zhou Yongsheng from China Foreign Affairs University.
Beijing appears to be showing the world that it is exercising restraint, but it also wants Tokyo to know that it is serious about the matter.
"And when Hong Kong activists do that job, China's sovereignty over the islands can still be shown because they are Chinese citizens," Zhou said. "Beijing is subtly telling Tokyo that China does not want confrontation, but Tokyo should not mistake Beijing's attitude as weakness."
On Wednesday, Chief Executive Leung Chun-ying summoned Japanese consul-general Yuji Kumamaru to urge Tokyo to release the eight activists who were arrested by Japan's coastguard. That was seen as a sign that Hong Kong was working in concert with Beijing. Shi Yinhong , an international relations professor at Renmin University of China, said the summoning of the consul, as the Foreign Ministry's protest, could influence Tokyo's handling of the matter.
Under the Basic Law, Beijing is responsible for foreign affairs issues that involve Hong Kong, but the chief executive can conduct relevant external affairs as authorised by Beijing.
A spokesman for Leung's office said it had informed the foreign ministry before summoning Kumamaru.
"The arrest of Hong Kong activists by Japanese authorities is a consular matter rather than a diplomatic matter," Shi said. "When Hong Kong residents are involved in trouble abroad, the chief executive has the obligation to make representations to the Japanese consul-general."
Leung's action bring to mind his predecessor Donald Tsang Yam-kuen's failed attempts to contact his Filipino counterpart during the hostage crisis in Manila two years ago.
When a Hong Kong tour group was held hostage on a coach, an anxious Tsang asked his staff to make two phone calls to Philippine President Benigno Aquino. Both times they spoke to an Aquino aide who did not manage to convey Tsang's message to Aquino. An effort to set up a phone call through the foreign secretary of the Philippines also failed.
Aquino later said that he did not expect Tsang to call that day. "Let's clarify. If a Philippine governor suddenly demands to speak with President Obama or President Hu Jintao , that would probably not be allowed," Aquino had said.
Veteran China watcher Johnny Lau Yui-siu said it was difficult to make direct comparisons between the two incidents because Leung was summoning a consul-general, not calling a national leader.
"We can still say that Leung is handling the matter quite well … it fits the procedure and nature of the matter," Lau said.
Ivan Choy Chi-keung, a political scientist at Chinese University, said Leung's handling of the issue was likely to help boost the chief executive's flagging popularity.
"Leung is someone who knows how to grasp public sentiment and improve his public image … but the prerequisite is that Beijing has allowed [things to happen this way]," Choy said.