Once a cocoa planter, Ferdinand Konan Yao has joined the ranks of fellow farmers who have abandoned Ivory Coast's top cash crop to work in clandestine gold mines buried deep in the plantations.

"It hasn't rained for more than five years and cocoa's no longer worth anything," said Yao, sporting a cowboy hat.

Ivory Coast is the world's leading cocoa exporter but it is the prospect of striking gold that is luring diggers from neighbouring Mali, Burkina Faso and Guinea.

They come to seek their fortunes in dozens of small unlicensed mines scattered over a radius of more than 300 kilometres (185 miles) in the central Nzi-Comoe region.

The work has also attracted thousands of cocoa planters, whose forebears had accomplished Ivory Coast's first "economic miracle" in the 1970s by hoisting the nation to top of the cocoa export list, ahead of other producers in Africa, Latin America and Asia.

Each morning, small groups of "peasant-miners" head across the wooded savannah carrying pickaxes, shovels and hoes to search for gold.

At work sites, broad trenches have been dug in the middle of plantations and uprooted trees lie in craters. The task of looking for gold is mobilising all able-bodied people from the former "cocoa belt".

At Boore, a village of 2,000 inhabitants in the central Dimbokro region, cocoa planter turned gold panner Octave Kouamee Konan openly regrets the destruction of an orchard.

"We were forced to do it," says the father of five children, seated on a felled tree trunk. "We had to choose between dying of hunger or feeding the family."

"In one week, I earn the equivalent of a year's cocoa harvest," he says.

Severe climate change that has struck the region is often blamed for the widespread abandonment of cocoa in favour of gold.

"Crops in this rich agricultural region are dependent on rainfall, which used to be abundant," Felix Kouassi, departmental director of agriculture in Bocanda, a regional town of more than 200,000 people, told AFP.

"The seasons have been out of whack for several years," Kouassi added. "In August we waited for the rains to get in a good harvest of yams and rice, but there has been none for several weeks."

- State shuts 200 informal mines -

At the end of a working day, nuggets are sold on site to dealers from Burkina Faso, Mali, Guinea and Lebanon for 20,000 CFA francs (about 31 euros) per gram. The earnings are shared out between the miner, the landowner and the person who loans the tools.

While cocoa remains the main export commodity, Ivorian authorities are keen to develop the mining industry, which at present accounts for just five percent of the gross domestic product.

Official industrial production of gold in Ivory Coast rose by 15 percent in 2015, reaching 23.5 tonnes compared with 20 tonnes the previous year. The steadily growing output relies on five mining operations.

The country's gold reserves are estimated at 600 tonnes, a figure that could be higher if prospecting by several companies bears fruit in the future.

But official production could be undermined by clandestine operations "on an enormous scale", according to an expert who referred to a study currently under way.

"It's a big challenge that Africa faces. Not only (Ivory Coast)," said Dennis Mark Bristow, the South African boss of Randgold Resources, whose company runs the largest mine in the country, at Tongon.

The biggest gold mine in neighbouring Ghana, at Oboassi, has been closed because of damage done by clandestine activity, Bristow notes.

To prevent such trouble, the Ivorian government has launched a "national programme for the rationalisation of gold mining", which led to the closure of 200 clandestine pits in the north and centre of the country.

This programme aims to "raise awareness among traditional chiefs and villagers who see gold washing as a source of income without evaluating the consequences", Minister of Industry and Mines Jean-Claude Brou recently said.

Alongside government measures, industrialists plan a unit for small-scale gold production, with "allocated corridors" and "work under some kind of law", Bristow said.

At present, illegal miners have turned from using mercury to cyanide in processing gold, he added. "They take the gold and leave the country. They are employing child labour, they don't abide by labour laws."

"It's important to work not to criminalise the project but to normalise it," Bristow added, stressing the commitment of mining firms listed on the London and New York stock exchanges to finding solutions and protecting the environment.