Massive floods have ravaged vast swathes of Asia\'s rice bowl, threatening to further drive up food prices and adding to the burden of farmers who are among the region\'s poorest, experts say.

A Cambodian boy rows a container through floodwaters in a village in Kandal province on October 3, 2011. More than 100 Cambodians, nearly half of them children, have died in the country\'s worst flooding in a decade, a disaster official said

About 1.5 million hectares (3.7 million acres) of paddy fields in Thailand, Vietnam, Cambodia and Laos have been damaged or are at risk from the worst floods to hit the region in years, officials say.

In Thailand, the world\'s biggest rice exporter, where 237 people have died in the floods, about one million hectares of paddy -- roughly 10 percent of the total -- have been damaged, they say.

Heavy rains in Laos and Cambodia have also led to big losses in recent weeks, and experts say flood waters have now drained into Vietnam\'s Mekong Delta, a key global rice producer, making it the latest to be inundated.

Further west, flooding of rice and other farmland in Pakistan\'s arable belt has cost that country nearly $2 billion in losses.

"The whole region will now suffer from rising food prices as potential harvests have now been devastated. The damage is very serious this year and it will be some time before people can resume normal lives," Margareta Wahlstrom, the United Nations chief of disaster reduction, said in a statement.

The flood damage comes on top of worries about the impact on global rice prices of a new scheme by the Thai government to boost the minimum price farmers receive for their crop.

Vietnam meanwhile is the world\'s number-two rice exporter and the Mekong Delta in southern Vietnam accounts for half the country\'s production.

"The upstream waters have begun to drop slightly but here they are rising three to five centimetres (1.2 to two inches) daily," said Duong Nghia Quoc, director of the agriculture department in Dong Thap province.

Dong Thap and neighbouring An Giang, which abut Cambodia, have been the worst affected in the delta.

The UN, citing government sources, says 11 people have died, more than 20,000 homes are flooded and 99,000 hectares of rice are at risk in Vietnam.

"Agricultural production is seriously affected this year by the floods that were, in fact, worse than our forecasts," said Vuong Huu Tien, of the flood and storm control department in An Giang, where thousands of soldiers have been mobilised to reinforce dykes and help residents reach safer ground.

In Cambodia, more than 330,000 hectares of rice paddy have been inundated, of which more than 100,000 hectares are completely destroyed, said a senior official at the Ministry of Agriculture.

Ngin Chhay said the "big loss" was likely to affect this year\'s rice surplus, which was expected to reach some three million tonnes.

Cambodia, where more than 160 people have been killed in the floods, exports only a fraction of total rice production but the crop accounts for about 7.5 percent of gross domestic product.

Laos, one of Asia\'s poorest nations, has also suffered, according to reports in state-controlled media there.

Tropical storms which struck since June killed at least 23 people in the country and damaged more than 60,000 hectares of paddy, the reports said.

In late September more crops suffered after a dam on a tributary of the Mekong released water to lower its rain-swollen levels, the Vientiane Times reported.

Vo Tong Xuan, a Vietnamese rice expert based in the Mekong Delta, said a major contributor to this year\'s floods has been the unusually heavy rains in Thailand and Laos, which drain down through the Mekong.

Experts say the delta\'s expanding system of dykes adds to the problem. They "prevent water circulation in some places but provoke floods in others," said Bui Minh Tang, a weather forecaster.

Vietnam News, the communist state\'s official English-language daily, reported that the lost rice crop in Dong Thap province alone was worth $2.7 million.

"The floods have seriously affected life and production of the farmers in our district, notably because of a shortage of drinking water and electricity," said Vu Tien Quang, who belongs to a farmers\' association in the province.