Thailand rice export prices plunged to a more than four-year low this week, pressured by excess domestic supplies, while rates in top exporter India fell for the first time in five weeks.

India's 5% broken parboiled variety was quoted at $359-$364 a tonne this week, its lowest since Sept. 30 and down from the last week's $364-$369.

"Demand is subdued as everyone is expecting fresh crop arrivals from December," said Nitin Gupta, vice president of Olam India's rice business.

In neighbouring Bangladesh, farmers said the production cost of rice could rise by as much as 30% because of higher diesel prices. The country last week raised diesel and kerosene prices by 23%, leading to a 27% increase in transport costs.

In Thailand, 5% broken rice prices fell to $377-$383 a tonne, a level not seen since October 2017 and down from $382-$384 last week.

Asia Rice: Export rates steady across hubs, ship scarcity worries Thai traders

Bangkok-based traders said low export volumes for most of 2021 have left an abundance of domestic supply, with new harvests looming towards the end of the year. They also reported new interest from old buyers, which could lead to sales.

"There's some demand that could boost export figures around the end of the year," one trader said. "It could be because Vietnam's end-of-season rice is expensive."

In Vietnam, 5% broken rice was unchanged from a week earlier at $430-$435 a tonne.

"Domestic supplies of fresh paddy are running low and this may put upward pressure on export prices over the next few months until the next harvest early next year," said a trader based in Ho Chi Minh City.

Farmers in the Mekong Delta provinces are sowing seeds for the winter-spring crop, the largest of the year, traders said.

Vietnam's rice exports in October rose from the previous month.