"We are calling on the generation of the 1989 massacre, both in China and overseas, as well as those who came before us and those who will come after us to work together and combine our strengths," the nine said in a joint statement read out by Wang Dan, one of China's most wanted men.
In Beijing, police sealed off Tiananmen Square for the anniversary with foreign journalists barred from the area.
At diplomatic level, China rejected a US call to investigate the massacre, and accused Washington of "political prejudices".
Open debate about the events of 4 June 1989, in which troops killed hundreds or even thousands of people during a pro-democracy demonstration, is forbidden in mainland China, and the government has never held an official inquiry.
When the UK returned Hong Kong to China in 1997, the territory retained its own legal system, including the right to protest.
Whether you like or not, the events ensured 20 years of fast economic growth
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