“We’re talking about 5,000 square kilometres under water,” said Mr Richard Horsey, a Bangkok-based spokesman with the United Nations office for Coordination of Humanitarian Affairs.
“The bottle-neck (in aid) is getting it out in the delta.
That needs boats, helicopters, trucks... There are upward of one million people in need of help,” he added.
Mr Horsey said there was a shortage of boats in the worst-hit areas of the lowlying Irrawaddy delta, with many vessels destroyed in the storm.
Without immediate assistance, the death toll — officially at nearly 22,000 with about 42,000 missing — would climb.
“We’re dealing with a situation where there could be a second round, where people start dying from water-borne diseases,” he told AFP.
“There are thousands of bodies floating around in the water,” he said, adding that they posed a grave health risk to the survivors.
Both France and the US have ships ready to deliver supplies after the devastating cyclone, but are awaiting the green light from Myanmar’s reclusive military, which appears reluctant to let in outside help.
A United Nation plane is currently in Brindisi in southern Italy waiting to fly to Yangon, while the UN refugee agency has 22 tonnes of aid poised on the Myanmar border, waiting for the go-ahead from the government.