Traders estimated Vietnam may already have sold about 8.33 million bags of coffee or about half of its crop. About half of the coffee grown in Daklak, the country's top growing province, has been picked, and farmers have also harvested up to 70 percent of the crop in the neighbouring province of Dak Nong, provincial agricultural officials said.

"The harvest is going smoothly as usual, thanks to the weather, with no rains, and it will end late next month," Nguyen Van Sinh, deputy director of Daklak's Agriculture Department, told Reuters on the sidelines of a cocoa conference.

Farmers in Buon Ma Thuot city, the capital of Daklak, and surrounding areas, began their harvest on Tuesday, which started out cloudy and windy but turned sunny at noon, providing favourable conditions for outdoor drying.

In Dak Nong, small coffee farms with limited finances will have to part with their stocks to get cash for bank loan repayments and investments in fertiliser for the next crop cycle, Nguyen Thanh Tung, head of the provincial Agricultural Department, said.

He said farmers were seeing average output to dip to 2 tonnes per hectare, from 2.5 tonnes in the previous season. A kilogram of robusta beans in Daklak rose to 27,700 dong ($1.72) on Tuesday from 27,200 dong on Monday and 26,900 dong a week ago, after London robusta futures closed firm and just below a five-week peak supported by investment fund buying.

Liffe's key March robusta contract closed $34 higher at $1,894 per tonne, after moving from $1,859 to $1,914. Traders estimated Vietnam's coffee output would fall slightly to 20 million bags from 21 million bags in the previous season