PHNOM PENH: The ruling Cambodian People's Party (CPP) declared a landslide victory in a one-sided election on Sunday, clearing the path for a historic leadership transition and the end of the reign of one of the world's longest-serving premiers.

The contest was effectively a one-horse race, with Prime Minister Hun Sen's CPP, a political behemoth with a vast war chest, facing no viable opponent after a ruthless, years-long crackdown that has seen hundreds of its rivals flee into exile.

The CPP was leading in ballot counting late on Sunday, with a turnout of 84%, according to the election committee, with 8.1 million people voting in a lopsided contest between the CPP and 17 mostly obscure parties.

"We've won in a landslide ... but we can't calculate the number of seats yet," CPP spokesperson Sok Eysan said.

Self-styled strongman Hun Sen, who has ruled Cambodia for 38 years, had brushed off Western concern about the election's credibility, determined to prevent any obstacle in his carefully calibrated transition to his anointed successor and eldest son, Hun Manet.

No timeframe had been given for the handover until Thursday, when Hun Sen, 70, signalled that Western-educated military general Hun Manet "could be" prime minister next month.

A National Assembly seat would makes him eligible, if backed by the house. Party spokesperson Sok Eysan said it was "very clear" Hun Manet won a seat.

Hun Manet has given few media interviews and no clues over his vision for Cambodia and its 16 million people.

He earned a master's degree at New York University and a doctorate at the University of Bristol, both in economics, and attended the West Point military academy, helping him rise through the ranks of Cambodia's military to army chief and deputy armed forces commander.

CLOSELY-WATCHED TRANSITION

Major powers will be watching closely for signs of whether Hun Manet will maintain the authoritarian status quo of his father or pursue greater liberalisation and a more Western style of democracy.

After casting his vote on Sunday, Hun Manet ducked questions about becoming premier and whether he would rule differently from his father.

"No comment please. I've just come to vote," he said in English, smiling.

Analysts had expected the transition to come mid-term, giving Hun Manet time to earn legitimacy with the public and political elite.

A key focus will be if he seeks to steer Cambodia out of the orbit of China and patch up ties with the United States that have perennially been strained by his father's iron-fisted approach.

A CPP rout was never in doubt after preemptive strikes by authorities that included disqualifying the CPP's only meaningful rival, the Candlelight Party, over a paperwork technicality.

Former Khmer Rouge guerrilla Hun Sen has been accused by activists of publicly threatening rivals and inciting violence, which led to Meta Platforms' oversight board recommending his suspension from Facebook. The government has denied persecuting opponents.

'COME OUT AND CONFESS'

The election committee also banned self-exiled opposition figurehead Sam Rainsy and 16 allies from elections for two decades for urging Cambodians to destroy ballots in protest.

Some did that, posting images of their ballots on social media, some with writing disparaging Hun Sen and calling him a coward. Another ballot said "U.N. pls help".

"The surprise of the day will be the number and the percentage of 'spoiled' ballots," Rainsy said on Twitter. "You can't win an election with no opposition."

Despite the CPP government's stranglehold over independent institutions, including the poll body, and allegations by activists of complicity in land grabs and environmental destruction, the party has consistently won the rural vote, reflecting improvements in basic infrastructure.

Its selling point has been ensuring peace and stability after decades of war, which spurred average growth of more than 7% until 2019, creating jobs in garment manufacturing and construction.

Hun Sen said the turnout, the highest in three decades, showed his "extremist" opponents had failed to derail the election. He urged those who destroyed ballots not to flee the country and suggested they own up.

"We already know your faces," he said on Telegram. "Don't be afraid, you may come out and confess ... otherwise, legal measures will be taken."