In white tuk-tuks kitted out with megaphones and banners, supporters of a tiny Cambodian opposition party wind down a dusty Phnom Penh street, rallying votes ahead of the country's one-sided election.

It will be a herculean task for the little-known Grassroots Democratic Party to win any seats in Cambodia's 125-member National Assembly in the July 23 election — widely dismissed as a sham.

But party president Yeng Virak insists his team is fighting the good fight. "We have a mission to restore democracy," he said.