Close supporters of Mr Yang in China, including relatives, believe that only Mr Yang's second wife, Yuan Rui Juan, and young child appeared in the arrivals lounge in Shanghai, Dr Feng said. Caption: Yang Hengjun left Sydney for Guangzhou on January 18. Friends of Mr Yang are concerned he was detained by Chinese government security officials before boarding his flight to Shanghai and that his wife was allowed to fly to Shanghai to look after her child. Dr Feng said that after taking her child to relatives, Mr Yang's wife then flew to Beijing and then back to Shanghai. There is no confirmation of exactly what has happened to Mr Yang. He is incommunicado and has not posted anything on social media including popular Chinese platform wechat since Friday. Australian diplomats overnight contacted Chinese officials but it is understood they were given little or no information and were unable to confirm if Mr Yang was being held by the Ministry of State Security.

"The Department of Foreign Affairs and Trade is seeking information about an Australian citizen who has been reported missing in China. Owing to our privacy obligations we will not provide further comment," a spokeswoman said. The Age and The Sydney Morning Herald called Mr Yang's Chinese phone numbers on Tuesday, but they did not connect. His wife's phone was also turned off. A relative's phone rang out. Dr Feng, who was detained for several days by Chinese authorities in early 2017, said that he had spoken to Chinese contacts with connections to the security services who said Mr Yang had been detained by the Ministry of State Security. Mystery about Mr Yang's whereabouts is especially unnerving for those close to him given the recent arrest of two Canadian men, Michael Kovrig and Michael Spavor, by Chinese police amid deteriorating relations between China and democratic countries. A friend of Mr Yang, China expert John Garnaut, said: "Let’s hope he reappears today and we can all agree there’s just been a misunderstanding. Nobody wants an Australian Michael Kovrig".

Loading Mr Yang has emerged as a popular writer and backer of democratisation and reform. He is critical of the authoritarian practices of the Chinese Communist Party. This is not the first time he has disappeared while visiting China. He was unreachable for several days during a 2011 trip, with those close to Mr Yang believing the Chinese secret police were responsible. He subsequently said the whole episode was a "misunderstanding". If it is confirmed that state security officials have detained Mr Yang, the Australian government would seek assurances from Beijing about his welfare and treatment because he is an Australian citizen. It is understood Mr Yang was seeking to bring his wife and young son to Australia under a family reunion visa. The Australian government would face an uphill battle advocating for Mr Yang.