Australian Foreign Minister Marise Payne said she was "very concerned" about the information she had received after a consular visit to the detainee revealed daily mistreatment and interrogation, Efe news reported.
"His circumstances of detention include increased isolation from the outside world, with restrictions on his communications with family and friends, and the resumption of daily interrogation, including while shackled," Payne said in a statement.
"This is unacceptable," she added.
The legal defence of Yang, a blogger and activist in favour of democracy in China, denounced that the authorities were subjecting him to this mistreatment to coerce him to confess to charges of espionage, which is punishable by death.
Yang, also a former Chinese Foreign Ministry official, was arrested in Guangzhou in January while on a stopover from the US to Australia, and was detained under a kind of house arrest without his location or charges being revealed.
Three months ago, Beijing confirmed to the Australian government that Yang had been formally charged with espionage on August 23.
Payne said that the Australian government had asked China to explain the charges against Yang and to respect his right to basic standards of justice, procedural fairness and humane treatment, including access to his lawyer and family as per international standards, "both of which continue to be denied to him".
"This has not led to any substantive changes in his treatment," the Minister underlined.
Beijing claims that the detainee's rights have been guaranteed and asked Australia to respect its judicial sovereignty and stop interfering with how it manages its cases.
Yang, who was a visiting scholar at Columbia University and lived with his family in New York, could face between three years of imprisonment and the death penalty if found guilty of espionage in China.
China has a long history of arresting dissidents, some of them while they are residing abroad, to later charge them with various crimes.
( With inputs from IANS )