From prominent celebrities to the Interpol chief, the world has seen millions of people in China seemingly vanish into thin air over the past few years — and yet the international community has remained largely silent.

Key points: Experts say the secret detentions violate international law and the silence needs to end

Experts say the secret detentions violate international law and the silence needs to end The international community has been urged to collectively put more pressure on Beijing

The international community has been urged to collectively put more pressure on Beijing Human Rights Watch says nobody is immune to being 'disappeared' by the Government

After taking power in 2013, Chinese President Xi Jinping introduced new laws that essentially made arbitrary and secret detentions legal under Chinese law.

These complex laws, as well as exceptions that can be used to strip detainees of their rights on the grounds of "national security", have been adjusted and expanded in recent years, with movie star Fan Bingbing and gene-editing scientist He Jiankui among the latest casualties.

Despite the high-profile disappearances, experts say many countries are reluctant to call Beijing out because of potential consequences.

Michael Caster, a China researcher and author of The People's Republic of the Disappeared, told the ABC that while true numbers are impossible to calculate due to the secrecy of the process, he estimates the numbers are "easily in the several hundreds", in addition to "upwards of a million Uyghur and minority group members".

He said those detained could be held for a few weeks, months or much longer. Occasionally they don't come back at all.

When they do come back, it is often to face court.

Mr Caster said most detentions included "extreme physical or mental abuse raising to the level of torture", with the main goal being to obtain a forced confession.

Experts say there is too much hesitance to call out China for fear of economic or political retaliation. ( Reuters: Thomas Peter )

But while Beijing has gone to great lengths to create a facade of legality, Mr Caster said this kind of detention violates international law and the "silence needs to end".

"There is too much hesitance to call out China for fear of economic or political retaliation," he said, adding that China had received "very little to no international blowback".

He said condemnation needed to come from a united front within the international community and go beyond individual cases to "challenge China on the institutionalisation of arbitrary and secret detention and widespread use of torture".

"You have a tremendous amount of power within the international coalition and coordination between states," he said.

"One state alone might not be able to stand up to China, but in concerted international pressure on China, there is power to push back against the false narratives of China when it tries to manipulate and bastardise what the rule of law means."

Maya Wang, a senior researcher for Human Rights Watch China, also urged foreign governments to put more pressure on Beijing and take a stronger stance on the state's crackdown on its ethnic Muslim-minority Uyghurs.

She added that no-one in China was immune to being "forcibly disappeared", whether they are a tycoon, a mega movie star or a bookseller.

Here we take a look at some of the high-profile cases of individuals who vanished over the past year, and where they are now.

Actress Fan Bingbing

Fan Bingbing has appeared in the X-Men and Iron Man film franchises. ( Reuters: Stephane Mahe )

Fan Bingbing, one of China's highest-paid actresses, appeared in X-Men and Iron Man films and once played a key role in one of China's propaganda films.

But that did not save her from being detained by Chinese authorities last June over alleged tax evasion.

Fan's 63 million fans on Chinese social media platform Weibo were shocked when the actress was quietly whisked away by Chinese authorities after a post emerged alleging that she had signed "split contracts", also known as "yin and yang" contracts, for the same job.

An article from state media Securities Daily in September said Fan was "placed under control", before the South China Morning Post reported she was under "residential surveillance" at a "holiday resort" in Jiangsu and had then been transferred to authorities in Beijing for further investigation.

For more than 100 days, her whereabouts was unknown and neither Fan nor authorities made any public statements explaining her disappearance.

In October, Fan finally re-emerged on Weibo and admitted that she signed "split contracts" for a film and other projects and apologised to the country and its citizens.

Since her reappearance, Fan has kept a low profile and is occasionally spotted in Beijing, where her entertainment firm is based.

Three Canadians detained

Businessman Michael Spavor, left, and former diplomat Michael Kovrig were detained in China in December. ( AP )

The detention of entrepreneur Michael Spavor and former diplomat Michael Kovrig in December came shortly after Canada arrested Meng Wanzhou, chief financial officer of Chinese telecommunications giant Huawei, in Vancouver at the request of the United States.

The Canadian Government said several times that it saw no explicit link between the arrest of Ms Meng, the daughter of Huawei's founder, and the detentions of Mr Kovrig and Mr Spavor.

But Beijing-based Western diplomats and former Canadian diplomats said they believed the detentions were a "tit-for-tat" reprisal by China.

Ms Meng is accused by the United States of misleading multinational banks about Iran-linked transactions, putting the banks at risk of violating US sanctions, while the two men were detained over suspicion of "endangering national security".

A third Canadian citizen, Sarah McIver, was detained two weeks later. Beijing said she was serving "administrative punishment" due to "illegal employment".

Canadian Prime Minister Justin Trudeau has been under pressure to take a more robust stand on the detentions, but said he would not be taking any drastic action.

Mr Kovig and Mr Spavor remain in detention, but Ms McIver was released last week.

Gene-editing scientist

The Chinese Government has launched a full investigation into Dr He and his research. ( AP: Kin Cheung )

Chinese scientist He Jiankui shocked the world after he announced in a YouTube video that he edited the genes of twin sisters, Nana and Lulu.

Hundreds of scientists, the Chinese Government and even his own university denounced Dr He for using a gene-editing technology known as CRISPR-Cas9 to alter the embryonic genes of twins in an attempt to protect them from infection with the HIV virus carried by their father.

An associate professor at Southern University of Science and Technology (SUST) in Shenzhen, Dr He defended himself at the Human Genome Editing Summit in Hong Kong in November — where he was last seen.

Dr He disappeared the following day and the ABC has attempted to call him several times without success.

While he still has not been seen in public, The New York Times published photographs of Dr He standing on the balcony of an apartment on the SUST grounds in late December.

Dr He's colleagues confirmed his identity after they saw the photos, The Times reported.

Citing Dr He's colleagues, The Times reported that Dr He is safe, but is believed to be under house arrest, guarded by at least 12 men in the apartment complex.

Former head of Interpol

Meng Hongwei was reported missing after traveling to China. ( AP: Wong Maye-E )

Former Interpol president Meng Hongwei, who was living with his wife and children in France, returned to his native China in September.

Mr Meng, who was also China's vice-minister for public security, was reported missing by his wife after he sent her a text of a knife emoji on September 29.

Chinese authorities have since announced that Mr Meng is suspected of bribery and other crimes, adding the investigation is partly due to him "bringing trouble upon himself".

The France-based Interpol has since elected a new Interpol president.

It was widely criticised for accepting a resignation letter apparently signed by Mr Meng, but provided by Beijing.

Award-winning photographer

Mr Lu's wife said he was taken away by state security agents. ( Xu Xiaoli )

Lu Guang's photography exposed the harsh realities of life for many in China until he was taken away, along with a fellow photographer, by Xinjiang state security on November 3.

His photos, which have won prestigious awards including a World Press Photo prize, tackled gritty subjects like pollution and industrial environmental destruction — issues traditionally avoided by the Chinese press because they risk punishment for exposing societal problems that the Government may consider sensitive.

Xinjiang authorities, who seized Mr Lu, have been at the forefront of a Government crackdown on Uyghurs and other Muslim minorities.

Thousands have allegedly been sent to indoctrination camps intended to sever their commitment to Islam and nurture loyalty to the Communist Party, and authorities there have a well-known intolerance for the media.

But Mr Lu's wife — who has still not received any information of her husband's whereabouts or what crime he is charged with — said he had not planned to conduct any photography projects in the province.

'Ink Splash Girl'

Ms Dong's father confirmed she was admitted to a psychiatric hospital. ( Twitter: @huayong798 )

Dong Yaoqiong disappeared on July 4 after splashing ink on Mr Xi's poster to protest the Chinese Government's "mind control persecution".

The 29-year-old was last seen live-streaming herself defacing the poster on Twitter before posting a photo purportedly showing police officers seen through an apartment peephole later on the same day.

A month later, a video released on Twitter showed her father Dong Jianbiao confirming she was admitted to a psychiatric institution.

"My wife signed a consent for my daughter's medical treatment, [but] wasn't aware of the real situation … I don't believe my daughter has [any] mental illness," Mr Dong said on Twitter.

Mr Dong said his request to visit his daughter was rejected by the hospital on July 22, and he didn't understand why his daughter's case was not handled by the police or the court, but by a mental institution.

High-profile church leader

Wang Yi, a high-profile pastor in China, was detained in December for subversion. ( Facebook: Early Rain Covenant Church )

As Mr Xi's crackdown on religion continues, Chinese authorities have reportedly detained more than 100 members of an unregistered Christian church and their pastor, Wang Yi.

Mr Wang was one of the Christian leaders who publicly criticised China's "war" on religion in recent years.

He also made reference to the Government's policies in Tibet and Xinjiang province respectively — two particularly sensitive topics for Chinese officials.

Enhui Cao, an Early Rain Church member who is also a teacher at the church's primary school, told the ABC the raids could be a result of Mr Wang's public criticism of China's new regulations on religious affairs.

"The pastor's joint submission is regarded as a disobedience … to the Chinese Communist Party's policy on the chinization of Christianity," Ms Cao told the ABC.

The church announced on its Facebook page that Mr Wang and his wife remained in custody, although a couple of other senior church leaders had been released but were still being monitored in their homes.

The Chinese Foreign Ministry has been contacted for comment but the ABC has yet to receive a reply.