Phnom Penh: Gullible Australians volunteering in Cambodian orphanages are unwittingly tearing families apart, an aid organisation says.

The number of orphanages in Cambodia has exploded to an estimated 600 in the past decade, despite a lack of conflict and social upheaval normally associated with such an increase.

Aid groups believe the trend is driven by dodgy operators exploiting poor families and deceiving foreigners to seek profits.

UNICEF estimates that only one in five children are legitimate orphans.

Friends International has launched a global campaign called `Don't Create More Orphans' aimed at educating people about the consequences of misguided generosity.