Prices for Vietnamese 5 percent broken rice fell to $485-$490 a tonne after remaining unchanged at $490-$495 a tonne for the past four weeks.

"Buyers are also switching to suppliers in Thailand and India where prices are comparatively cheaper than Vietnam’s," a trader based in Ho Chi Minh City said, adding exporters were also put off by high shipping costs.

After successfully containing the virus for most of last year, infections have recently risen in Vietnam.

"Local sales are slow due to the expansion of a new Covid-19 outbreak that has hit some rice-growing provinces in the Mekong Delta," the trader added.

Vietnam’s rice exports in the first five months of 2021 likely fell 11.3 percent from a year earlier.

Prices for top exporter India's 5 percent broken parboiled variety were unchanged for a second consecutive week at $382-$388 per tonne.

Farmers are prepping paddy seedlings, an exporter said, as monsoon arrived over Kerala, marking the start of the four-month rainy season crucial for the farm-dependent economy.

"If a huge volume was imported, that could flood local markets and hurt farmers," a senior food ministry official said.

In Thailand, prices for 5 percent broken rice fell to $457-$468 per tonne from $457-$485 last week.

High fuel prices were translating into more expensive freight, while also making it difficult for exporters to secure container ships to ferry their cargo, traders said.

Overseas demand remained low because of the high prices, while an anticipated rise in supply in the second half of 2021 could lower current prices, traders said.