The Cambodian opposition politician has been told she is on a list of 10 people who are next in line to be arrested. Hers is no idle fear.

In the early hours of last Sunday, the president of her Cambodian National Rescue Party, Kem Sokha, was handcuffed during a raid on his home and taken away to a remote prison.

Other Cambodian opposition leaders have also been jailed, gone into hiding or are too afraid to speak out, as part of a sweeping campaign of intimidation, harassment and arrests.

Officials of Prime Minister Hun Sen's ruling party have warned that more arrests are to come.

As Australia still tries to convince asylum seekers on Manus Island and Nauru that Cambodia is a functioning democracy, and a place they can call home as part of its $55 million refugee deal, in Cambodia, an atmosphere of fear is pervasive.

The Cambodia Daily - which was forced by the government to shut down this week - described the country in its final edition as embarking on a "Descent Into Outright Dictatorship".

Sochua, one of the opposition party's three vice-presidents, is a quietly spoken and respected figure in Cambodian politics who was orphaned by the murderous Khmer Rouge.

While most opposition figures have been silenced by fear, she accuses Hun Sen of abandoning any pretence of democracy to crush his political opponents and critics ahead of national elections next year.

"It's not about me. I fear for Cambodia. You can take away our freedom. But you can't take away our conviction, hope and faith for a better Cambodia," she says.

Her voice is trembling with emotion. Sochua says she has written a statement to be released to the United Nations, Australia and other countries if she is taken into custody.

"Millions of Cambodians are concerned about the future of their democracy. We appeal to Australia and other countries to help us."

Hun Sen has cracked down in the past, only to pull back so that generous donor countries would continue to pour in more than $US1 billion a year to help Cambodia's mostly impoverished 16 million people.

But this crackdown is unprecedented since the former commander in the Khmer Rouge army staged a bloody coup in 1997 to remove co-prime minister Prince Norodom Ranariddh.

Cambodian author and US-based university professor Ear Sophal says the last vestige of Western political liberalism has been extinguished.

"Rest in peace, democracy," he says. "It was a nice, one-generation ride."

Threats and surveillance

Despite a $55 million aid deal signed in 2014, Australia has so far sent only a handful of refugees from Nauru to Cambodia, even though they have been promised a land of opportunity with mosques, jobs, football and martial arts.

Now the Turnbull government has begun a fresh push to convince refugees on the Pacific island to relocate to Cambodia.

"Up until now Australia has been seen to be sending refugees to a poor democratic nation," says a Phnom Penh-based human rights activist, who asked not to be named, fearing government reprisal.

"But suddenly the deal is sending refugees to a dictatorship. Is that acceptable to the Australian people?"

Almost every day a Cambodian government-aligned website, Fresh News, whips up sentiment, publishing unsubstantiated claims that opposition members, their families, journalists, staff of foreign NGOs and the CIA, among others, are plotting regime change.

Hun Sen has publicly declared he would be willing to "eliminate 100 to 200 people" to protect national security and told the opposition to prepare coffins for themselves.

Staffs of Cambodia's largest pro-democracy NGOs and their families have been receiving threats for months. They complain of being followed by armed guards or police and having their homes put under surveillance.

"We are watching you," Hun Sen warned in a speech.

The campaign of fear intensified in mid-August, when the government shut down the partly US and Australian-funded National Democratic Institute and expelled its staff. The government accused the organisation of not being "neutral and independent" and failing to comply with local laws.

And the government slapped a huge $US6.3 million dollar tax bill on the award-winning Cambodia Daily, one of the country's few investigative news outlets, while Hun Sen branded its publisher a thief.

Thirty-two radio stations broadcasting US government-funded Radio Free Asia, Voice of Democracy and Voice of America have been shut down or restricted, reducing access to independent foreign-sourced news for millions of Cambodians, particularly in rural areas.

Laws and regulations have been passed curbing trade unions and imposing restrictions on opposition political parties.

Human rights groups are calling for an independent investigation into the broad daylight murder last year of Kem Ley, a popular social commentator and frequent government critic.

Jailing of Tep Vanny

For years Hun Sen has been using the criminal justice system to further the objectives of his ruling Cambodian People's Party, and billionaire cronies, by jailing social activists such as Tep Vanny, a mother of two who has become a symbol of a struggle against repression.

Tep Vanny and a group known as the "women of the lake" have for 10 years fought the eviction of as many as 20,000 people from their homes on 133 hectares of land that was once Boeung Kak Lake. The land was signed over to a company linked to a powerful politician from Hun Sen's party to build luxury condominiums.

For the supposed crime of calling for protests to continue over Cambodia's most notorious land dispute, Tep Vanny was jailed last year, and with other long-dormant cases involving anti-government protests piling up, she faces years in prison.

Human rights activists say no credible evidence has been presented to back any of the charges brought against her.

"I miss my mother very much," says Ou Kung Panha, 13, sitting in her grandmother's dirt-floor house opposite the lake. "She is very brave and I am proud of her."

Panha suffers convulsions and wakes up screaming at night over the jailing of her mother.

Sy Heap, 68, appealed for authorities to release her daughter despite being scared of reprisals.

"My daughter has done nothing except speak about what is right, but authorities are trying to destroy my family," says Heap, who has only a small income from selling cigarettes and gasoline. "It's unjust."

Tep Vanny, always defiant, wrote in a letter smuggled from jail that she had to wear a prison uniform and was handcuffed like a criminal as well as being "smeared" by the courts and government.

Trump as inspiration

The closure of the Cambodia Daily after 24 years of publication on September 4 sparked an outcry from politicians as well as human rights activists and media organisations around the world.

The last story its reporters covered was the storming of opposition leader Kem Sokha's house by up to 200 police shortly after midnight on September 3.

"They are trying to shut down all independent voices," says Jodie DeJonge, the Daily's editor-in-chief. "We have been a burr in Hun Sen's side for the entire time we have been operating."

The loss-making newspaper only sold about 5000 copies a day but its reporting on issues such as illegal logging and land evictions made it influential among Phnom Penh's educated elite, students and foreigners.

Hun Sen was once able to hold the newspaper and its rival, the Phnom Penh Post, up to aid donors as evidence of free media.

Now he doesn't seem to care, citing Donald Trump's attacks on the US media to justify his own actions.

Amid a meteoric rise of access to the internet, authorities are cracking down on social media users such as Facebook.

More than 70 per cent of Cambodians are now users of social media and opposition parties have employed it in the past to mobilise support.

A woman who posted a 13-second video on Facebook showing her throwing a shoe at a logo bearing a picture of Hun Sen is one of at least half a dozen social media users who have been jailed. A man was jailed for two years for simply posting an image of an effigy of Hun Sen.

Rumours of terminal illness

Rumours that Hun Sen has a terminal illness that swept social media were fuelled in part by photographs of him as a patient in a Singapore hospital.

But such speculation appears to be wishful thinking by his opponents. According to several reliable sources, Hun Sen underwent surgery for a compressed disc in his back.

The Prime Minister, who has already ruled for three decades, insists he intends to remain in power for at least another 10 years.

A foreign NGO worker who has lived in Cambodia for years says Hun Sen is moving to tighten his grip on power after only winning the 2013 elections, marred by voting irregularities, by a narrow margin.

Local elections in June delivered the ruling party only a six per cent winning margin, a shock result.

The NGO worker says Hun Sen has great political survival skills but is paranoid that the tide of public opinion is turning against him.

"I wouldn't say he is a good chess player because if he was losing he would pick up the chess board and throw it against the wall," he says.

Hun Sen commands a more than 6000-strong personal bodyguard based near his fortress-like residence outside Phnom Penh, which bristles with sophisticated military hardware, including rocket launchers and 100 tanks.

The military, which receives training and support from the Australian Defence Force, regularly deploys to back the ruling party's political actions.

Defence Minister Tea Banh has repeatedly warned that soldiers would "smash the teeth" of protesters and side with the ruling party in any conflict. Military commanders publicly condemn opposition figures.

'Saviour of the nation'

Hun Sen, who defected from the Khmer Rouge and joined invading Vietnamese troops to remove the regime from power in 1978-9, sees himself as saviour of the nation, and has warned that an opposition election victory would lead to civil war.

Multiple vested interests are prepared to strongly back him, concerned that if he loses they would also lose their own wealth and influence.

Known for his fiery criticism of the United States, Hun Sen has in recent days stepped up his anti-Western rhetoric, accusing Washington and unnamed foreign powers of trying to stir up an Arab Spring-style revolt to topple his government.

He has also been strengthening ties with China, which offers aid and investment with no strings attached that dwarfs the $US80 million annual contribution from the United States.

While for years Hun Sen had to walk a tightrope to appease Western donors, he now sees no reason to pay lip service to human rights and political freedoms. Relations with the US have become toxic. Earlier this year, he suspended joint military exercises with the US and Australia.

"Because Donald Trump has demonstrated little interest in promoting human rights and democratic processes, Cambodia is off the hook," says Carl Thayer, an expert on Cambodia from the Australian Defence Force Academy.

Opposition leader Kem Sokha has been accused of conspiring with a foreign power, based on a speech that he gave in Adelaide four years ago referring to support he had received from the US. He faces 15 to 30 years in prison.

Human rights groups have described the arrest as outrageous.

Sochua, one of her party's three vice-presidents, called on donor countries such as Australia - which played a key role nearly three decades ago in brokering an end to years of civil war - to stand up for Cambodian democracy.

She says the international community should make it very clear that there must be a level playing field for all political parties ahead of the elections. She wants Australia to convene an urgent meeting of signatory countries to the 1991 Paris Peace Accords to examine Hun Sen's recent behaviour.

The accords were supposed to enshrine political freedoms in the country where at least 1.7 million people died under the Khmer Rouge's genocide.

Sochua fears that unless Australia and other countries have the courage and conviction to speak out against the Hun Sen regime, repression will worsen.

"We need hope that democracy here has a chance," she says. "But a red line has already been crossed."