Rice export prices in India fell this week to their lowest this year.
It happened before top buyer Bangladesh slaps import duty on exports of the grain after domestic production recovered, reports Reuters.
Rates for India's 5.0 per cent broken parboiled variety fell by $6 to $393-$397 per tonne.
Bangladesh is imposing tax at the rate of 28 per cent on rice imports to support its farmers after local production revived, Finance Minister Abul Maal Abdul Muhith said on Thursday.
He said 25 per cent customs duty and 3.0 per cent regulatory duty would be imposed on rice imports.
Indian exporters said they were going to lose competitiveness due to the duty hike.
India was the biggest supplier of rice to Bangladesh in 2017.
"Exports to Bangladesh would become nearly impossible if it raises the import duty," said an exporter based at Kakinada in the southern state of Andhra Pradesh.
In Vietnam, prices of 5.0 per cent broken rice climbed to their highest since January 2012, at $465-$475 a tonne.
The prices were $455-$460 a week earlier.
"Prices are too high for any deals to be clinched while supplies remain tight, though the spring-summer harvest has begun," a Ho chi Minh City-based trader said.
Output from the ongoing harvest is low while the rice quality is not very high, traders and farmers in southern Vietnam said.
"Exporters are now only looking at government-to-government deals," the trader said, adding that the Vietnamese government was not buying output from the current harvest for stockpiling.
Elsewhere in southeast Asia, Thailand's benchmark 5.0 per cent broken rice slipped to $430-432 per tonne compared with $430-446 last week.
Thai rice traders said demand has been flat with no new interest registered from overseas this week.
"We probably have to wait until after Ramadan to see if there is fresh demand from Africa," a Bangkok-based trader said.
African markets usually import parboiled rice from Thailand every year.
The same trader said the demand from there has slowed in the first half of this year.
Thailand's commerce ministry this week said the country exported 4.98 million tonnes of rice during the period of January 01-June 01 this year.