A letter written by an Australian-Chinese political commentator in 2011 has been released to the media, after he instructed a friend to publish it if he disappeared.
Yang Hengjun, a political commentator and writer, was detained on January 19 and is being held in Beijing under suspicion he is endangering China's national security.
The letter, penned eight years ago, was given to Mr Yang's close friend, Australian academic Dr Feng Chongyi.
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When it became apparent Mr Yang was not being released soon, Dr Feng followed his instructions and released it to the media, reports 7 News.
It urges activists to "maintain belief in China's democratic future, and, when it doesn't put yourself or your family at risk, to use all your means to push China's democratic development to happen sooner".
He asks his supporters to push for "freedom, human rights, the rule of law and justice to occur sooner" in China.
Most ominously, he writes: "If I can come out, I will continue my work. If I cannot come out, or disappear again, remember my articles and let your children read them."
His letter also highlights the importance of democracy, and has a message of hope.
"I really believe that in China, spreading the philosophy [of democracy] is a vital task. I will definitely continue to use my methods to contribute to China's democracy."
Mr Yang was detained in Guangzhou earlier this month, and is believed to be under residential surveillance in Beijing.