Billions of dollars' worth of gold is smuggled out of Africa each year, much of it bound for Dubai before it is legally re-exported to other countries, a Swiss NGO said Thursday.

Development NGO Swissaid published a report saying that 321-474 tonnes of African gold produced through artisanal and small-scale mining goes undeclared each year, representing a value of between $24-$35 billion.

Africa is the world's main gold-producing continent, with Ghana, South Africa, Mali and Burkina Faso leading production in 2022.

According to the NGO, smuggling of African gold is on the rise, having "more than doubled between 2012 and 2022".

The NGO said the precious metal was "a source of income for millions of artisanal miners, the main source of revenue for many governments, a means of financing armed groups, and the cause of serious human rights violations and environmental degradation".

The report singled out Dubai as an international hub for trade in African gold, which then makes its way to countries including Switzerland.

The NGO estimates that in 2022, "66.5 percent (405 tonnes) of the gold imported into the UAE from Africa was smuggled out of African countries".

It arrives in Dubai by plane, "in hand luggage or in the hold, on scheduled flights or in private jets."

The emirate is home to gold refineries and thousands of precious metal and gemstone traders.

From there, African gold is sent mainly to Switzerland, its "second-largest importer", and also to India.

Under Swiss law, the last place where the gold is processed is its place of origin, so that gold arriving in Switzerland is not traced back to Africa, the NGO explained.

The report covers the period from 2012 to 2022 and is based on data collected from 54 African countries, cross-referencing gold production data with official export and import data.