Cambodians are voting in an election that will not feature the only serious challenger to the rule of Prime Minister Hun Sen, who has been in power since 1985.
Critics have called the vote a sham as the Cambodia National Rescue Party, which narrowly lost the last election, has been dissolved.
The US and EU are among those who have questioned the credibility of the vote.
But the ruling Cambodian People’s Party says 19 other parties are standing.
On Friday, the Cambodian government ordered internet service providers in the country to block a number of independent news websites, including Radio Free Asia, Voice of America and Voice of Democracy.
It also singled out a post on the German version of the image-sharing site Pinterest, which had specifically referenced the Cambodia National Rescue Party.
English newspaper outlets were among other sites blocked.
As part of a large UN peacekeeping mission, Cambodia held its first multi-party elections in decades in 1993 after years of bloodshed and war. Some two million people are estimated to have died between 1975 and 1979 when the country was ruled by the radical communists of the Khmer Rouge.
Hun Sen, a former soldier in the Khmer Rouge who later opposed them, has presided over a sustained period of rapid economic growth.
He has long been accused of using the courts and security forces to crush dissent and intimidate critics, but has for years allowed some measure of political opposition to his CPP party.
This election however marks the “death” of democracy in Cambodia, senior opposition figure Mu Sochua told the BBC.
Analysts say that a key test for Hun Sen’s legitimacy will be how many voters turn out. During the campaign, opposition activists calling for a voter boycott have been accused of incitement.
Voters dip their finger in indelible ink at polling stations, making it easy for local authorities to see who has voted, and who has not.
A voter in the southern province of Kampot told BBC Thai that he would vote “just to have ink” on his finger.
“I’m afraid there could be problems and I will be arrested,” the 39-year-old man, who did not want be named due to fear of retribution, said.
In 2013, the Cambodia National Rescue Party (CNRP) led a mass protest movement after rejecting the election results, posing the biggest threat to Hun Sen’s rule in more than a decade.
It was allowed to contest local elections last year, and won around 44% of the popular vote.
Since then, its leader has been jailed for alleged treason, and much of its senior leadership has fled abroad, trying to drum up support for international sanctions. Independent media outlets have closed or left the country and journalists have been arrested.
The party itself was dissolved in November by the Supreme Court, based on a complaint from the government that it was conspiring with the US to overthrow it. All its elected politicians lost their positions, including 55 seats in the 123-seat National Assembly.
On Friday, during the last day of campaigning, Hun Sen told thousands of supporters that his party had eliminated “traitors who attempted to topple the government” .
“If we didn’t eliminate them with an iron fist, maybe by now Cambodia would be in a situation of war,” he said.
The US and the EU, which both lavished aid on Cambodia after its first UN-administered election in 1993, have cut off electoral assistance for this poll.
But China, which recently gave more than $130m in military aid to Cambodia, is sending observers for the first time.