Friends of an Australian citizen detained in China are concerned he was initially denied his choice of lawyer because Australian diplomats provided him a limited list of firms to choose from.

Key points: Prominent political blogger Yang Hengjun is accused of "endangering state security"

Prominent political blogger Yang Hengjun is accused of "endangering state security" Mr Yang could be detained in China for six months before he is "formally" arrested

Mr Yang could be detained in China for six months before he is "formally" arrested Australian officials were not allowed to ask Mr Yang why he reportedly rejected a lawyer appointed by his wife

Australian writer Yang Hengjun, 53, has been held in a secret location in Beijing for more than five weeks and is accused of "endangering state security".

The broad and vague allegation could see him detained for half a year before prosecutors are even obliged to "formally" arrest him.

Family, friends and supporters are increasingly concerned the Australian Government is approaching the highly sensitive case too timidly and is not advocating strongly enough for Mr Yang.

On Tuesday this week, a consular official from the Australian embassy was permitted to make a second visit to Mr Yang, who was described as being in very good health and spirits despite his detention.

Yang Hengjun has been in detention for over five weeks. ( Twitter: Yang Hengjun )

Friends in contact with Mr Yang's family said the Australian consular official said she was not permitted by Chinese authorities handling the case to ask Mr Yang exactly what charges he is facing.

According to messages seen by the ABC, she also said she was not allowed to ask why he had rejected a lawyer appointed by his wife.

Earlier this month, Chinese state security officials informed Mr Yang's friend, prominent Beijing-based lawyer Mo Shaoping, that Mr Yang had rejected his application to represent him.

During the second consular meeting, Mr Yang did express that he wanted Mo Shaoping's firm to take his case, according to his friends and family.

No answers given

Now, according to a letter written by Mr Yang from detention and obtained by the ABC, he appointed an Australian lawyer from a list provided by the Australian consular official during the first visit in late January.

His supporters are questioning whether Mr Yang was even aware Mr Mo sought to represent him during the initial visit.

Mr Mo's firm was not on the list of law firms provided by the Australian embassy, and friends are asking why the embassy did not inform Mr Yang his wife had already arranged for Mr Mo to take his case.

A lawyer from Mr Mo's office, Zhang Dongshuo, told the ABC the firm is usually on lists of law firms provided by both the US and Canadian embassies to their detained nationals in China.

In a statement, the Department of Foreign Affairs and Trade (DFAT) said "the issue of legal representation was discussed" during the second consular visit.

"Australia remains concerned that Mr Yang has not had access to legal representation during his detention, as we would for any Australian who is detained for lengthy periods of time overseas," the statement said.

DFAT declined to answer more specific questions.

According to Mr Yang's letter, he has appointed Sydney-based Australian lawyer Lin Tang.

The contact and address details of Mr Tang's representative office in Beijing provided on the list were out of date, and a representative for the firm in Sydney said the Beijing office had closed, although Mr Tang himself is currently in China.

Mr Tang did not immediately respond to a request for confirmation that he was handling the case.

Barred from the outside world

Australian consular officials also informed Mr Yang's family he was receiving medication for high blood pressure, and said he was being provided with daily necessities but was not permitted to watch television or read newspapers.

His wife has been barred from visiting him in detention.

Mr Yang previously had a career in China's government before obtaining Australian citizenship in the early 2000s and becoming a prominent political blogger online.

In recent years he was based in the US as a visiting scholar at Columbia University and flew to China on January 19 to spend the Lunar New Year with his wife's family.

Sorry, this video has expired Chinese-Australians concerned after Yang Hengjun detainment

He then planned to move back to Australia with his wife, who has been told by authorities to remain in China.

China's Ministry of State Security is handling the case and is notoriously secretive with media.

China's Foreign Ministry has provided little detail except to confirm the case is an investigation for endangering state security and that Mr Yang's rights under Chinese law are being protected.

China's state media has largely stayed silent on the case, but a prominent editor, Hu Xijin, has publicly suggested Mr Yang's case is likely an isolated one and not related to broader issues in the Australia-China relationship.

Editor's note March 13, 2019: An earlier version of this story said that Australian diplomats failed to tell Yang Hengjun that his wife had appointed a specific lawyer to his case. The ABC has since been made aware that the issue of the specific lawyer was brought up in a second meeting with consular officials.