GENEVA, Dec. 2 (Xinhua) -- Devastating monsoon rains and tropical cyclones have unleashed catastrophic flooding across parts of South and Southeast Asia, killing hundreds of people, displacing communities and causing major economic disruption, the World Meteorological Organization (WMO) said Tuesday.

Clare Nullis, a WMO official, told a UN press briefing in Geneva that Indonesia, the Philippines, Thailand, Viet Nam and Sri Lanka are among the worst hit, as monsoon-related downpours combine with tropical typhoons.

Floods remain among the region's top hazards, and rising temperatures are increasing the likelihood of more intense rainfall, she warned.

In Sumatra, Indonesia, national authorities report more than 600 deaths and over 460 people missing, with over 1.5 million people affected.

Viet Nam has been battered for weeks, with some areas receiving more than 1,000 millimetres of rain and historic and tourist sites badly damaged. A meteorological station in Hue City recorded 1,739.6 mm of rain in 24 hours in late October, a new national record that could be the second-highest 24-hour total ever measured in the Northern Hemisphere and Asia. The country has registered 98 deaths and 10 missing.

The Philippines, still recovering from earlier typhoons, is facing another storm, while in Sri Lanka nearly one million people have been affected and more than 400 reported dead or missing after Cyclonic Storm Ditwah triggered record floods and landslides. Sri Lanka has declared a national disaster, saying it has not seen such severe conditions in years.

Ricardo Pires, for the United Nations Children's Fund (UNICEF), said more than 275,000 children have been affected by Cyclone Ditwah, which brought severe flooding and landslides after making landfall on the east coast of Asia on Nov. 28. With many areas still inaccessible, the true figure could be higher, he added.

The disaster highlighted the need to further strengthen regional forecasting systems, expand coping capacities and increase data sharing, Nullis said.

The Asia-Pacific region is facing the world's record typhoon activity, and no single institution or country can deal with tropical cyclones or climate change alone, she said. ■