Photo/IllutrationIn this image from video, Chinese Foreign Ministry spokesman Lu Kang speaks during a media briefing in which he commented on investigations into Chinese-Australian writer Yang Hengjun in Beijing on July 18. (AP Photo)

CANBERRA--Australia's foreign minister said on Friday her government was "deeply disappointed" that a Chinese-Australian writer had been placed in criminal detention in Beijing six months after he was taken into custody at a Chinese airport.

Foreign Minister Marise Payne said that China had normally notified her government that spy novelist and former Chinese diplomat Yang Hengjun had been taken into criminal detention.

"The Australian government is deeply disappointed that Australian citizen and academic Dr. Yang Hengjun ... has been transferred to criminal detention in China," Payne said in a statement.

"The Australian government is concerned by this development in relation to an Australian citizen. We will continue to press Chinese authorities for fair and humane treatment, in accordance with international norms," she said.

The 53-year-old visiting scholar at Columbia University in New York has been detained since Jan. 19, when he arrived from New York at China's Guangzhou Airport with his wife Yuan Xiaoliang, and his 14-year-old stepdaughter.

Yang's Beijing-based lawyer Mo Shaoping said Yang's wife received notice on Wednesday that the Ministry of State Security in Beijing transferred him to criminal detention.

Yang had previously been held under so-called residential surveillance at a designated location. This can involve being guarded 24 hours a day with lights on continuously and tortures including sleep deprivation, being tied to a chair or forced to stand for hours.

Yang is now suspected of endangering national security--a major crime that includes 19 individual offenses such as spying. Mo said the crime he is suspected of is much more sweeping, whereas espionage was very specific.

Yang has not been formally charged. He has been moved to a detention center in Beijing, where his case is being investigated, Mo said.

The investigative agency must decide whether to approve his formal arrest. This could happen within 37 days, or the agency could apply for more time, Mo said.

Payne said her government had raised its concerns about Yang's case regularly with China at senior levels. Australian Embassy officials have visited Yang six times, most recently on June 27.

"I have written twice to China's Foreign Minister, State Councilor Wang Yi, to request a fair and transparent resolution to this matter and that Dr. Yang be granted access to his lawyers. This has not occurred," Payne said.

"The government has expressed concern about Dr. Yang's welfare and the conditions under which he is held. And we have asked for clarification regarding the reasons for Dr. Yang's detention. If he is being detained for his political views, then he should be released," she added.

Yang's friend, University of Technology Sydney academic Feng Chongyi, on Friday congratulated Payne for what he described as "the strong statement I have been asking for."

Feng suspects Yang was detained in retaliation for the December arrest of Meng Wanzhou, the chief financial officer of Chinese tech giant Huawei, in Canada on a U.S. warrant. The arrests of two Canadians in China were widely suspected as such, and Payne has previously said her government would be concerned if Yang's detention was related to the other cases.

Feng, who was detained for two weeks in 2017 while visiting China to research human rights lawyers, said on Thursday Australia should work with other countries including the United States and Britain to stop China for taking such retaliation against other nations' citizens.