The Australian government is asking Beijing for information about a former Chinese diplomat turned democracy activist allegedly detained by a group of ten security agents shortly after landing at an airport in China on Saturday.

Yang Hengjun, who was born in China but gained Australian citizenship, left New York a day before with his wife and a child, but reportedly failed to catch the second leg of the journey onward to Shanghai, according to a witness speaking to The Australian newspaper.

Australia’s department of foreign affairs and trade confirmed on Wednesday it was “seeking information about an Australian citizen who has been reported missing in China”.

Friends have feared for Mr Yang’s safety as he has been conspicuously silent online; an active and influential commentator, he hasn’t posted on Twitter since January 17. Mr Yang worked for China’s foreign ministry before taking Australian citizenship and growing more outspoken on a spate of issues relating to the Chinese government. He was previously detained by Chinese authorities in 2011.

“Dr Yang is not only brilliant but extraordinarily popular among the Chinese speaking world,” tweeted John Garnaut, a China expert and friend of Mr Yang, describing him as a “courageous and committed democrat”.

“This will reverberate globally, if authorities do not quickly find an off-ramp,” Mr Garnaut wrote.