The family of an Australian writer jailed in China are calling on their government to urgently secure his release, warning he "may be dying".
Yang Hengjun has been detained for almost five years on espionage allegations denied by him and Canberra.
His sons have written to Prime Minister Anthony Albanese ahead of the leader's landmark visit to Beijing this weekend, which aims to improve ties.
Dr Yang was secretly tried in 2021, and his charges have not been made public.
His sons - who had remained silent about his detention until now - say they were "inspired" to act after the recent release of Australian journalist Cheng Lei.
"We ask that you make clear that it is not possible to stabilise the bilateral relationship with a government that is holding an Australian citizen just a few kilometres south of where you will be hosted," the letter says.
It urges Mr Albanese to "do all in your power to save our father's life", saying Dr Yang's health has "rapidly declined" in recent weeks.
Mr Albanese will be the first Australian leader to visit China since 2016, following a series of prickly disputes which led to the suspension of high-level meetings.
He lands in Beijing on Saturday and will meet Chinese President Xi Jinping and Premier Li Qiang during his trip.
Dr Yang, who previously worked for China's Ministry of State Security, was a scholar and novelist in Australia who blogged about Chinese affairs. He was nicknamed the "democracy peddler", but his writings often avoided direct criticisms of the government.
The 57-year-old was intercepted at Guangzhou airport in January 2019 and accused of spying. His case has mostly unfolded behind closed doors since then.
Australian officials have previously raised concerns, but China's foreign ministry has warned them not to interfere in the case, and to respect the nation's "judicial sovereignty".
Dr Yang has been subjected to "more than 300 interrogations" and "six months of intense torture" while in detention, his family says.
In August, he learnt he had a large cyst on a kidney. "He said for the past 3 weeks he couldn't walk and remained basically bedridden and even had difficulty walking 4 metres from his bed to the toilet in his cell," the letter reads.
It claims the cyst was identified in health checks when Dr Yang was first detained but Chinese authorities had "never told him" about it.
"Still he does not know whether the kidney cyst or something else is causing him to repeatedly collapse. He does not know whether the pills prescribed to him each day are designed to make him better."
The letter also included quotes from Dr Yang, taken from a recent consular report.
"I'm sick, I'm weak, I'm dying… I just hope I will be able to get out alive," he pleaded.
