Widespread flooding has forced over 85,000 people from their homes in Burma.
The worst affected area is the Irrawaddy Delta, the same region devastated by cyclone Nargis in 2008.
Around 70,000 people have been displaced in the delta and are being housed at 219 emergency relief centres set up at schools and monasteries.
Annual monsoon rains often cause flooding in the region, but emergency response teams have said this year's are the heaviest since 2004.
"The floods have actually affected half of the country," Denis De Poerck, the director of operations for the charity Save the Children in Burma, told Radio Australia's program.
"This one is really massive . . . People are describing it as a very huge catastrophe," he said.
At lease 600,000 acres of rice fields across the country have been swamped.
"Most of the rice fields of so many people who depend on agriculture for their livelihoods have been flooded and this will have a very severe impact on their income for the months to come," Mr De Perck added.
Several bridges and rail lines have also been damaged, but there are no reports of casualties yet.
© ABC 2012
13:39 EST With 28mm already recorded in the rain gauge this month, Alice Springs is having its wettest May since 2004.