There have been calls for Australia to withdraw funding to Cambodia after the country's Supreme Court dissolved the main opposition party, dealing a crushing blow to democratic aspirations in the south-east Asian nation.

Key points: The 118 opposition party members will also be banned from politics for the next five years

The 118 opposition party members will also be banned from politics for the next five years The Government accuses the Cambodia National Rescue Party of plotting a coup

The Government accuses the Cambodia National Rescue Party of plotting a coup CNRP's director of public affairs, Kem Monovithya, urges the Australian Government to act immediately

Kem Monovithya, director of public affairs for the opposition Cambodian National Rescue Party (CNRP) and daughter of jailed opposition leader Kem Sokha, told the ABC that if countries like Australia and the US did not respond they would become "accomplices in the destruction of democracy".

"What we need now is action from the international community," Ms Monovithya told The World program.

"I am urging, I am calling on, in particular the Australian Government to immediately send the message to the Cambodian Government that Australia is no longer going to fund the election, is no longer going to endorse the 2018 election."

"It's not a time for statements, it's time for action.

"Pulling back the election support now. Starting from Australia, EU, Japan and the US."

Rights groups backed calls for countries to reconsider their engagements with Cambodia.

"The misuse of the courts to dissolve the CNRP is one of the gravest threats to human rights and representative democracy modern Cambodia has seen," said Kingsley Abbot of the Geneva-based International Commission of Jurists.

"[That] should be acknowledged as such by the international community when it sits down to consider its political and economic engagement with the country."

There has been a growing push from Hun Sen's administration to neutralise political opponents. ( Reuters: Samrang Pring )

Supreme Court reaches unanimous verdict

The Supreme Court decision clears the way for the nation's authoritarian leader, Prime Minister Hun Sen, to remain in power for years to come.

The verdict, which was widely expected, comes amid a growing push by the administration of Hun Sen to neutralise political opponents and silence critics ahead of elections due in July 2018.

Chief Judge Dith Munty, who is a senior ruling party member, announced the nine-member court's unanimous ruling.

He said 118 opposition party members would also be banned from politics for the next five years, and the verdict could not be appealed.

In a televised address, Hun Sen told Cambodians the election would go ahead "as normal" and called on CNRP members who had not been banned to defect to his party.

The Government accuses the CNRP of plotting a coup and has called for its dissolution for weeks.

The nine-member Supreme Court made a unanimous ruling. ( AP: Heng Sinith )

The opposition staunchly denies the allegations and says they are politically motivated — a position backed by international rights groups and independent analysts who say no credible evidence has emerged to back the claims.

The party had been expected to pose a serious challenge in next year's polls. During the last vote in 2013, it scored major gains in a tense race that saw Hun Sen narrowly retain office.

Since then, the opposition's fortunes have ebbed dramatically.

Vows to continue 'fight for democracy'

Sam Rainsy, who led the party during that vote, went into exile in 2016 and faces a jail term for a criminal defamation conviction if he returns.

The party's current leader, Kem Sokha, has been imprisoned since September, charged with treason.

Opposition leader Kem Sokha has been in jail since September. ( Reuters: Samrang Pring )

Amid deepening fears over the nation's fate, more than 20 opposition parliamentary members — about half of those with seats in Parliament — have also fled the country.

Mu Sochua, an opposition party vice-president who is among those who have left, said the struggle for democracy was not over in Cambodia.

"But in the heart, in our hearts, in our minds, in our spirits, in our souls, the fight for democracy will continue. It will not die," she said.

The Government-led crackdown, which has intensified over the past few months, has targeted civil society groups and independent media outlets, too.

Hun Sen has been in office since 1985 and has held a tight grip on power since ousting a co-prime minister in a bloody 1997 coup.

Although Cambodia is nominally a democratic state, its institutions remain fragile and the rule of law weak; the judiciary is not seen as independent.

The 2018 election had been shaping as possibly the biggest challenge to Hun Sen's leadership, after his opponents united behind the CNRP. They had made significant gains in local elections in June.

ABC/Wires