In a single week in January, two Australian men were swiftly arrested in Asia.

Key points: Australia often engages in "quiet diplomacy" with authoritarian governments in Asia

Australia often engages in "quiet diplomacy" with authoritarian governments in Asia The Government has criticised China but remained silent on Vietnam

The Government has criticised China but remained silent on Vietnam Ethnic origin, and the complexity of cases, can affect how the public reacts

Both faced trumped-up charges of threatening national security in communist regimes.

One case — that of 54-year-old Yang Hengjun, a writer and pro-democracy activist of Chinese heritage — has evoked strong condemnation from the Australian Government.

The second, involving retiree Van Kham Chau, a 70-year-old pro-democracy activist, has not.

Dr Yang was first detained in mid-January and later accused of espionage. Chau was also arrested in mid-January after meeting with a local dissident and charged with trying to overthrow the state. That was later reduced to "terrorism".

Chau, a member of the activist group Viet Tan, which Vietnam considers a terrorist group, was convicted and sentenced to 12 years in prison in a trial lasting less than five hours.

Dr Yang has yet to face China's courts.

Foreign Minister Marise Payne called Dr Yang's treatment "unacceptable" and said she was "very concerned" about reports he is being shackled during daily interrogations — treatment that "might be tantamount to torture", according to his Australian-based lawyer Rob Stary.

Yang Hengjun with his wife Xiaoliang Yuan, who was interrogated and banned from flying home. ( Supplied )

The most Senator Payne or the Department of Foreign Affairs and Trade (DFAT) will say publicly about Chau's case is that they are offering "consular assistance".

When asked why her response was different in the two cases, Senator Payne repeated her previous comment that "it would be inappropriate and not in Mr Chau's best interests to comment while legal processes remain available".

Prime Minister Scott Morrison has rubbished the suggestion that Dr Yang is a spy. He has not done the same for the suggestion Chau is a terrorist — a claim Chau's son Daniel says is "ludicrous".

Mr Morrison has told Chau's family Australia cannot interfere in another country's legal matters and that the Government would "continue to regularly engage" with the Vietnamese Government on his case.

The disconnect hasn't escaped the notice of Human Rights Watch's Australia director Elaine Pearson, who wrote to Senator Payne this week.

Australian citizen Van Kham Chau was sentenced to 12 years' jail in Vietnam. ( Supplied: HRW )

"Payne has rightly condemned the detention conditions of the Australian writer Yang Hengjun and urged his release, so it is puzzling that there has been no similar statement raising concerns about Chau Van Kham's treatment even though he has been detained since January," she said.

"There are serious concerns about lack of due process and the severity of the sentences, following what can only be described as a 'show trial'."

Vietnam's Ministry of Foreign Affairs told the ABC the trial against Chau and "accomplices of the Viet Tan terrorist group proceeded in an open and transparent manner, in accordance with the procedures and regulations of the Vietnamese law, ensuring in full the rights of the defendants".

Is race a factor?

Both Dr Yang and Chau are Australians of Asian descent, but would our public reaction to both cases be more vocal if their names were Steve or Bob?

That's what Chau's wife Quynh Trang Truong suggested in a letter to Mr Morrison last month.

Mr Chau's son Daniel and wife Trang say the idea of Mr Chau being a terrorist is "ludicrous". ( ABC News: Mazoe Ford )

"Whist I understand your diplomatic position, one would have to wonder if my husband were a white Australian that the intervention might not be so weak or reluctant to date," she wrote.

When the ABC published its first story on Chau's arrest in February, many people questioned Chau's Australianness on Facebook.

Under a picture of Chau and a headline detailing how the Australian citizen was being investigated for a crime that could potentially carry the death penalty, comments started to appear: "I can't see an Australian in that photo!"

Australian journalist Peter Greste spent more than a year in an Egyptian prison. ( AAP: Dave Hunt )

The case of former Al Jazeera journalist Peter Greste offers a stark comparison to the arrest of Australian man Hazem Hamouda — both were arrested and held for more than a year in Egypt, but it's likely you've never heard of Mr Hamouda.

His daughter, Lamisse, told the ABC it was difficult for Australians with an ethnic background who were locked up overseas.

"There's an immediate sense of, 'oh, well, you're already bit different. That's your country anyway'," she said.

"I really think there is a big difference between how an Australian with an ethnic background is treated versus, perhaps, a white Australian.

"[It] really uncomfortably highlights the existing racial tension already within Australia itself and within its sense of identity."

The fight to free Mr Hamouda, left, was draining, his daughter Lamisse, right, says. ( Supplied: Lamisse Hamouda )

Ms Hamouda said dealing with governments in a bid to free her father, who was released in April, was "very delicate territory" because "you don't want to create any more trouble".

Ms Hamouda's father was freed in April. ( ABC News: Talissa Siganto )

"But to not have visible government support, or to have very limited and muted government support, does affect your morale," she said.

But ethnic origin isn't the only factor — how complex a case is can affect whether it captures the popular imagination.

Ms Hamouda watched the case of Bahraini refugee Hakeem al-Arabi unfold and saw the intense media scrutiny surrounding his detention in Thailand. At that time, her father had been imprisoned for almost a year.

"I was so happy to see [Hakeem] get such public support, but then it contrasted quite sharply with the lack of publicity around my own father's case. And it did leave me questioning, 'who deserves support, and who doesn't?'"

There was high-profile advocacy in al-Arabi's case — retired soccer player Craig Foster became an outspoken advocate for his release, and there was the question of Australia's bureaucratic bungle leading him to be locked up in the first place.

Quiet diplomacy — does it work?

Diplomats often tend to take a softly-softly approach to dealing with governments in Asia on human rights.

Part of this, the argument goes, is that to admonish another country publicly would embarrass them or make them "lose face", potentially exacerbating the problem and being counterproductive to securing their citizen's release.

Yuan Ruijuan says the investigation into her husband is ongoing and he remains detained in Beijing. ( AP: Chongyi Feng )

Catherine Renshaw, deputy head of the Thomas More Law School at the Australian Catholic University, said public denunciations were often for domestic audiences in Australia, rather than trying to sway foreign governments.

"The theory is that megaphone diplomacy — publicly signalling strong disapproval about the actions of a particular state — is not very effective with authoritarian states [like both China and Vietnam]," she said in an email.

She said there was often concern that foreign governments would "dig in" and that public statements could make things worse for political prisoners.

That doesn't mean there isn't value in calling out abusive human rights situations overseas, she added, saying in some cases "silence can be just craven and shameful".

Carl Thayer, emeritus professor at the defence force academy at the University of New South Wales, said Australia had a positive relationship with Vietnam, in contrast to our tempestuous relations with China, which could account for why DFAT has been more vocal in Dr Yang's case than Chau's.

"Vietnam's arrest and detention of Chau cannot be viewed as politically motivated against the Australian Government," he wrote in a briefing note earlier this year.

"This contrasts with Australia's current testy relations with China and the very high likelihood the arrest of Yang Hengjun on charges of espionage was deliberately engineered by Chinese Government officials to signal displeasure with the Morrison Government."

He added Dr Yang's case followed the pattern of politically-motivated arrests, including those of two Canadians and a British former diplomat, amid strained relations over Huawei.

Australia was more willing to make "public recriminations" in Dr Yang's case, Mr Thayer said, because China had come out swinging and there were other "irritants", like foreign interference and China's treatment of Uyghurs.

"It's China that's doing the pushing — cutting off coal, banning MPs from visiting, criticising us openly … and therefore there's less of a political price to pay [than with Vietnam]," he said.

Van Kham Chau was sentenced to 12 years in jail for conducting activities of "terrorism to oppose the people's administration". ( AP: Nguyen Thanh Chung/VNA )

Human Rights Watch's Elaine Pearson said there was "a time and a place for quiet diplomacy", but in Chau's case, it wasn't working.

"It just emboldened the Vietnamese Government to hand down very severe sentences for peaceful political activity," she said.

Former Socceroos captain Craig Foster campaigned for Hakeem al-Araibi's release. ( ABC News: Danielle Bonica )

"The problem with quiet diplomacy is that it lets governments off the hook, there is no accountability."

Mr Thayer told the ABC that as Australia has recently strengthened relations with Vietnam, it was "a good time to use this uptick in relations to get a result quietly".

He said the Government shouldn't shut their mouths in the hopes of getting more trade, as trade relations were solid. Chau's son Dennis previously criticised Australia for focusing more on trade than on the human rights of its citizens during a human rights dialogue between the two nations.

There is another important point of difference complicating matters in Chau's case — it's believed he entered Vietnam on a fake ID.

Viet Tan's chairman has said that activists sometimes resort to such measures when they believe they are on a blacklist, but the detail makes it more difficult for everyday Australians to grasp.

But Mr Thayer points out it's important to ask "does the punishment fit the crime?" Ultimately, Chau was convicted of terrorism alone — any allegations of forgery or illegal entry were not aired at his trial.

Vietnam maintains "Viet Tan is a terrorist group that has made multiple attempts to infiltrate people and arms into Vietnam with the aim to sabotage, riot, incite hatred among Vietnamese nationals and cause social instability".

Vigils calling for Chau's release were held in Sydney in September. ( Supplied )

With Christmas approaching, Chau's wife and sons are feeling the sting of his absence, their Australia-based lawyer Dan Phuong Nguyen told the ABC.

His wife expressed gratitude to politicians and DFAT officials she met in Canberra recently, who offered words of comfort and raised awareness of the case.

But Ms Nguyen said, despite reassurances in private, Chau's wife was saddened that there was still no strong public comment from the Government about her husband's plight.