Indonesia's grade 4 defect 80 robusta in Lampung, the main coffee growing province, was steady at a $140 a tonne premium to London's May contract, the same level it has stayed at for six weeks, a Lampung-based trader said.

But trade picked up as more stocks arrive during a mini harvest, while the main harvest is due later this year.

"Coffee trading is increasingly busy from week to week," the trader said, adding there is an estimated 180 truck loads that had been traded, each carrying up to 10 tonnes of beans, with around half of those were on Thursday alone.

Meanwhile, coffee market in Vietnam, the world's top robusta bean producer, remained subdued as buyers stayed clear, eyeing beans from the harvests in Indonesia and Brazil.

"It is a very strange year this year," said Phan Hung Anh, deputy director of Anh Minh Co, a coffee-trading firm in Daklak, Vietnam's largest coffee-growing province.

Farmers quoted beans at 36,800-37,000 dong ($1.61-$1.62) a kilogram in Dak Lak province, decreasing slightly from 37,500 dong a week ago, as London prices fell sharply.

The London May contract dropped as much as 4 percent on March 23 to $1,671 a tonne, but prices have recovered slightly since, albeit at a slow pace.

Vietnamese traders quoted the 5 percent black and broken grade 2 robusta at a discount of $40 to the May contract, or at a $70 discount to the July contract, but only few contracts were signed.

"Farmers don't really need cash now, and they have about 25-30 percent of stock left and prefer to keep them to be safe," said Le Duc Huy, vice general director of Simexco, a top exporter in Daklak.

Vietnam is seen exporting 180,000 tonnes of coffee in March, bringing exports of the beans in the first quarter of this year to 510,000 tonnes, or a 12.7 percent increase from the same period last year, official data on Thursday showed.

The country exported nearly 130,000 tonnes in February, when it had a long holiday break, and shipped around 200,000 tonnes of coffee in January.