Coffee trading in Indonesia picked up slightly ahead of a mini harvest expected from March, while Vietnam's market was dull following a major holiday, traders said on Thursday.

Indonesia's grade 4 defect 80 robusta traded at a premium of $140 a tonne to London's May contract, compared to a $160 premium to the March contract two weeks earlier, a trader in Lampung said.

"Trade is starting to pick up (this week) because some areas are already starting to have early coffee harvest," the trader said.

Some areas in Indonesia's Sumatra island usually have a mini harvest around March and April, while the main coffee harvest normally starts in July.

In Vietnam, the world's top robusta bean producer, trade was slow after the Lunar New Year celebration, the country's biggest holiday locally known as Tet. Traders estimate farmers have sold 40 to 50 percent of their crop so far.

Farmers in Daklak, Vietnam's main coffee-growing province, quoted beans at 37,000-37,600 dong ($1.63-$1.65) per kg, expanding from a 37,000-37,200 dong range before Tet, traders said.

Traders quoted the 5 percent black and broken grade 2 robusta at a discount of $50-$100 per tonne to the ICE May futures contract , barely unchanged from a range of $60-$100 per tonne prior to the holiday.

Trade is expected to pick up in the next few days when farmers and coffee companies workers are fully back to work, traders said.