Farmers and up-country buyers said the dip was due to the late arrival of seasonal rains, adding that harvesting of the main crop in the world's fifth biggest producer would likely continue longer than last season as a result.

The arrivals figure was based on estimates from three international exporters based in the port city, Douala. Five buyers contacted by Reuters confirmed the drop in output.

"Last year between August and December, I had bought 200 tonnes. This year I'm at 100 tonnes for the same period," said Valere Nszie, an independent buyer in the village of Nkolmelen, between the capital Yaounde and the town of Ntui.

Cameroon's marketing season opens in August and runs to July, with the bulk of the harvesting done during a main crop from August to January.

"Buyers who last year were doing 1,800 tonnes this year aren't able to supply 500 tonnes," said Clovis Kameni, a buyer in Ntui for local Barry Callebaut unit SIC Cacaos.

The late arrival of the rains was likely to extend this season's main crop, farmers and buyers said. But they warned that the additional harvesting would not necessarily close the production gap on last year.

"Last year the harvest ended around Jan. 15 but this year it will finish at the end of January," said Vendelin Ntingah, who farms three hectares near the village of Minkama 3.

Cameroon produced around 231,000 tonnes of beans during the 2016/17 season, the National Cocoa and Coffee Board said.