The inundation, which affected Cambodia, Laos, the Philippines, Thailand and Vietnam, has triggered a "major supply shock" and curbed the region's gross domestic product by about 0.9 percent, the UN Economic and Social Commission for Asia and the Pacific (ESCAP) said in a statement.

Thailand is the world's second largest maker of hard disk drives so the floods could affect global notebook computer production in early 2012, it said.

Thai farms have also been severely affected, with about 7.0 percent of regional rice production and about 1.4 percent of global production damaged.

The UN agency predicted that growth in developing countries in the Asia-Pacific region would slow to 6.6 percent in 2012, from an estimated 7.2 percent this year.

"The Asia Pacific region is facing the challenge of coping with a sharp deterioration in the global economic environment," ESCAP chief economist Nagesh Kumar told a news conference.

"Despite the decline of course the Asia-Pacific region will continue to remain the most dynamic in the world," he added.

Thai economic growth is expected to rebound to 4.5 percent next year thanks to a post-flood recovery, from 2.0 percent in 2011.

But regional powerhouse China is projected to see growth fall to 8.5 percent, from 9.3 percent, the UN said.

More than 1,000 people have died in massive floods across Southeast Asia in recent months and millions of homes and livelihoods have been destroyed.

The floods are expected to curb growth by 1.3 percentage points in Thailand this year, and by 0.3 percent each in Laos, Myanmar and the Philippines, according to ESCAP.