China's foreign ministry spokesman says Australia is trying to interfere with its "judicial sovereignty" after Foreign Affairs Minister Marise Payne called for the immediate release of writer Yang Hengjun.
Dr Yang has been held by Chinese authorities for three years since being detained at Guangzhou airport in January 2019.
The Australian national is awaiting a verdict following a one-day espionage trial, which took place in Beijing last year.
Dr Yang, 56, is a democracy advocate who has said authorities "treat me like dirt here and they tortured me".
Ms Payne's call for his release came after friends of the writer feared his growing health problems would lead to him dying behind bars.
During the daily press briefing on Tuesday, China's foreign ministry spokesman Zhao Lijian said Dr Yang was being treated fairly.
"China's judicial organs handle the case in strict accordance with law and fully protect the lawful rights and interests of Yang Hengjun," Mr Zhao said.
Dr Yang is believed to be suffering severe problems with gout, high blood pressure, impaired vision and dizzy spells.
Recent blood tests have revealed rising levels of creatinine, prompting fears Dr Yang could suffer kidney failure, but a Chinese prison doctor has been unable to provide any treatment or advice on treatment.
Ms Payne said the federal government was concerned for Dr Yang.
"Neither Dr Yang nor the Australian government have been provided with details as to the charges against him or of the investigation, reinforcing our view that this constitutes the arbitrary detention of an Australian citizen," she said.
"We therefore call for Dr Yang's immediate release and his return to Australia.
"Australia is also extremely concerned about Dr Yang's health. We call on Chinese authorities to meet their obligations to ensure that all necessary treatment for his physical and mental health is provided."
