With rice stored from the previous harvest likely badly damaged as well, it was critical to get farmers back on the land to plant a new crop, FAO regional chief He Changchui told Reuters.

"There is not much time. The planting season has started already. We need to have the funds and resources to bring the farmers back," He Changchui said in an interview.

"The consequence is very clear that we might have food shortages if we don't plant today," he said, estimating a 50-day window to get the crop planted.

Myanmar's agriculture ministry says it needs $243 million for rice seed, fertiliser and to rehabilitate paddy fields after the cyclone flooded 5,000 sq km (1,931 sq mile) in the delta.

The ministry estimated 650,000 hectares of paddy mainly in delta and around the former capital of Yangon were damaged out of a total 3.2 million hectares, He Changchui said.

Some of the funds raised from donors will go towards buying 97,000 tonnes of seed, including 6,000 tonnes of salt-tolerant varieties, he said.

With monsoon rains on the way, the FAO hopes they will wash away much of the salt left by the cyclone's 12 foot (3.5 metres) sea surge which inundated prime rice-growing areas in the delta.

Although the former Burma could face a serious shortage of rice, some media reports of a risk of famine were premature.

"We do not have data to support this kind of assessment," He Changchui said.

The world's largest rice exporter when it won independence from Britain in 1948, Myanmar surrendered that title to neighbour Thailand after four decades of disastrous economic policies by the ruling military.

With little money to buy other food, people consume on average 44 lbs of rice per month, compared with 35 lbs in Vietnam and 15 lbs in Asia as a whole, the FAO said.

Myanmar was expected to export 600,000 tonnes of rice this year based on the amount the government had allowed exporters to buy from farmers for sale abroad.

"If we miss the opportunity to plant this season, instead of exporting, maybe they will have to import," he said. "That's why we have a serious concern about food security."