An Australian writer Yang Hengjun were formally detained in China on suspicion of espionage and is being held in “harsh conditions”, the Australian government said on Tuesday.

Yang, who was born in China, was detained in the southern city of Guangzhou in January amid growing tension between Australia and its largest trading partner.

“We have serious concerns for Dr Yang’s welfare, and about the conditions under which he is being been held,” Foreign Minister Marise Payne said in a statement.

“Yang was held in Beijing in harsh conditions without charge for more than seven months. Since that time, China has not explained the reasons for Yang’s detention, nor has it allowed him access to his lawyers or family visits,” she added.

The Foreign Minister said she had discussed the issue twice with her Chinese counterpart, Wang Yi, and had also written to him three times to express her concern about the health and wellbeing of the 53-year-old academic and pro-democracy activist.

Yang’s Australian lawyer, Robert Stary, was not available for comment.

Yang, 53, whose legal name is Yang Jun, was detained in China while waiting for a transfer to Shanghai, after flying in from New York.