PHNOM PENH - At the Toul Kork Primary School in Phnom Penh volunteers swept classrooms and laid out wooden desks on Saturday, transforming the rooms into polling stations a day ahead of a general election which Prime Minister Hun Sen is expected to comfortably win.Election committee officials at the primary school in Boeung Kak 1 commune say 8,135 people are registered to vote there."I believe voters will come out to vote," Yos Vanthan, head of the school's election committee, told Reuters.Nineteen political parties are running against Hun Sen's ruling Cambodian People's Party (CPP) but none are strongly critical of the prime minister or the government. His main challenge, the opposition Cambodia National Rescue Party (CNRP) was dissolved by the Supreme Court last year and many of its lawmakers banned from politics for five years.Hun Sen, a former Khmer Rouge commander who eventually defected from Pol Pot's murderous regime, is the world's longest serving prime minister.Many CNRP leaders have fled abroad and are living in self-imposed exile and its leader, Kem Sokha, was jailed in September on treason charges, leaving Hun Sen, who has ruled for 33 years, with no significant opponent.Some Western countries and the United Nations have questioned the credibility of the election because of the lack of any significant competitor to the CPP. Rights groups have also criticized restrictions placed on independent media and civil society.The CPP has urged people to vote, despite calls from CNRP leaders to boycott the election. A low-voter turnout could undermine the CPP's claims to legitimacy.Dim Sovannarom, a spokesman for the National Election Committee, who inspected the school on Saturday, said the commission expects more than 60 percent of registered voters to cast their ballot.Nearly 70 percent cast their ballot during the last general election in 2013."We expect more than 60 percent in the whole country," Dim Sovannarom told reporters, before unveiling grey metal polling boxes donated by the Japanese government.Critics, including exiled opposition members, have called for targeted sanctions against Hun Sen's government and its allies following the pre-election crackdown.Mu Sochua, CNRP deputy president, said any country that does not denounce the election cannot call itself democratic."Any country supporting, or that is hesitant to denounce the election as a sham, should not call itself on the side of democracy," Mu Sochua told Reuters.On Wednesday, the US House of Representatives passed a long-awaited Cambodia Democracy Act, paving the way for sanctions to be imposed against Hun Sen's inner circle.This week Japan said it would not send observers to the election despite doing so in numerous elections in the past.Voting is not mandatory in Cambodia, but authorities have warned that anyone who boycotts the vote will be seen as a "traitor."All the same, some said they will not show up."Why should I vote? It makes no difference," said an airport taxi driver who hails from the southwestern province of Takeo.He declined to be named for fear of repercussions.