The children of a jailed Australian in China are pleading with Anthony Albanese to help bring their father home as the prime minister visits Beijing.

Yang Hengjun was arrested in August 2019 on suspicion of espionage, and has spent more than four years in a Beijing prison.

For the first time since the academic was detained, a letter he wrote for his two sons in Australia was delivered to them last week after he received a consular visit by an Australian official.

They have requested their identities remain publicly hidden.

Mr Albanese will travel to Beijing next week where he will meet with Chinese President Xi Jinping, in a sign of thawing relations between the two nations.

In a letter to the prime minister, Dr Yang’s two sons urge Mr Albanese to act and use this “narrow window of opportunity” to help secure their father’s release.

“We request that you do all in your power to save our father’s life and return him immediately to family and freedom in Australia,” they wrote.

“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.”

In August, Dr Yang was told by medical authorities they had discovered a massive 10cm cyst on his kidney.

Fearing for their father’s life, his children at the time urged the government demand the pro-democracy writer be given medical parole or access to Australian-supervised care outside of his detention centre.

A consular report written last Wednesday said Dr Yang’s “physical condition had declined,” that he looked pale and had lost weight.

It said Dr Yang had reported a new doctor had prescribed him three vitamin pills and added an egg to his daily diet as treatment.

His sons wrote two elements of Dr Yang’s imprisonment were “particularly cruel”.

These included his enforced confinement for a man “full of life and energy and completely incapable of sitting still” and being deprived of his love of reading and writing.

Opposition foreign affairs spokesman Simon Birmingham said securing Dr Yang’s release should be one of the top priorities of the prime minister during his visit to China.

“It will not be possible for Australians to believe those relations have been fully stabilised whilst an Australian citizen continues to face such detention,” he told ABC Radio on Wednesday.

“He has now spent more than four years detained by China without any transparency around the nature of his charges and with continuous delays in terms of the sentencing of him.”

Dr Yang previously wrote he had been denied direct sunlight for more than four years apart from some rays that occasionally came through panes of glass.

His children wrote their father was in jail because he represented truth, democracy and the rational exchange of ideas.

They say Dr Yang had been subjected to more than 300 interrogations over 18 months, including six months of intense torture.

The writer was deprived of sleep, and had his wrists and ankles strapped to a chair for days at a time until he couldn’t walk.

Dr Yang’s children say Mr Albanese’s efforts to free Cheng Lei sent a message to Australia’s Chinese community that the nation upheld its citizens’ rights regardless of their ethnicity.

Senator Birmingham said it was also critical for Mr Albanese to raise Chinese trade sanctions during the meeting with President Xi, describing the tariffs as economic coercion.

“Wine producers shouldn’t have to wait for a five-month review to learn whether the sanctions, the tariffs against them will be lifted,” he said.

China agreed to review its sanctions on wine following almost three years of the tariffs being in place.

Australia had dropped its dispute with the World Trade Organisation in response to the Chinese review.