The number of child brides in Africa will more than double to 310 million by 2050 unless urgent action is taken, the UN's children's fund Unicef has warned in a new report.
More than one in three girls are married before the age of 18, mostly in poor rural families, it said.
The projection was based on slow rates of reduction and rapid population growth across the continent.
The African Union (AU) wants to set 18 years as the minimum age for marriage.
The AU launched a campaign earlier this year to end the practice of child marriage and its head, Nkosazana Dlamini-Zuma, told the BBC that the practice can "oppress women".
"It's something we are dead against in every country as we don't think children should be wives," she added.
The report says the percentage of young girls in Africa who are married before the age of 18 has fallen from 44% in 1990 to 34% today.
But massive population growth means there will still be an increase in the number under-age marriages unless far more ambitious action is taken, it added.
Africa's population of girls under 18 is predicted to rise from 275 million today - 25% of the global total - to 465 million by 2050, 38% of the total.
<<Print>>