The Sunday vote in more than 1,600 communes -- village clusters -- comes after months of political tension in the fragile democracy, where Hun Sen is accused of crushing dissent after nearly losing the last 2013 poll.
The opposition movement has been hit hard by his crackdown and the June 4 vote is seen as barometer for its chances of turfing Hun Sen out at next year's general election.
In a possible sign of nerves over the vote, Hun Sen broke with his tradition of avoiding the campaign trail to lead a massive parade of trucks, motorcycles and tuk-tuks through the capital today.
Addressing a sea of flag-waving supporters dressed in the ruling party's signature baby blue, Hun Sen delivered a well- worn speech about the stability he has brought to Cambodia since the end of the genocidal Khmer Rouge regime.
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"Which party brought about peace?" he asked a raucous crowd decked out in shirts, hats and flags bearing the emblem of his Cambodian People's Party (CPP).
Hun Sen, himself a Khmer Rouge commander, later defected and joined the Vietnam-backed government that ousted the brutal regime.
Over more than three decades in office he has curried favour with the bureaucracy, security services and many older Cambodians, who connect with the 64-year-old's populist wit and narrative as a stabilising force after the Khmer Rouge horrors.
Hun Sen has frequently warned that war would break out if his party is ousted in elections.
"CNRP is the party of the future," opposition leader Kem Sokha told a crowd of cheering supporters waving flags with the party's rising sun emblem.
The party nearly unseated the premier in a 2013 poll and claims it only lost due to voter fraud.
Yet the movement has been dented by Hun Sen's subsequent crackdown, with at least 27 Cambodian human rights defenders and political activists thrown behind bars since 2013, according to a recent Amnesty International report.
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