(Corrects in paragraph 8 to ...120 million ..., not 120.)

NEW DELHI, April 3 (Reuters) - South Asian leaders must act immediately against the threat of rising sea levels and river salinity due to global warming, which endangers millions of poor people in the region, a top Bangladesh official said on Tuesday.

"Bangladesh urges immediate collective action and stronger regional cooperation for the conservation and utilisation of our shared environment," Fakhruddin Ahmed, chief adviser to the Bangladesh government, said at a summit of South Asian leaders.

Low-lying Bangladesh, with more than 140 million people, is one of the world's most densely populated nations. It is also one of the most ill-prepared to face global warming and very likely to be among the nations worst affected, experts say.

Millions of people live along the largely flat delta bound by the Bay of Bengal to the south. As sea levels rise and storms increase in number and severity, vast areas of land could be swallowed by the sea.

Rising sea levels due to global warming and an alarming intrusion of salinity into the region's river channels were all impending threats that needed to be addressed, said Ahmed.

"The lives and livelihood of our peoples are adversely affected because of these looming environmental crises," he told delegates from eight nations at the opening of the 14th summit of the South Asian Association for Regional Cooperation, or SAARC.

A draft of a United Nations report due on Friday has warned that rising temperatures will result in a drop in crop yields and increase the risk of hunger in Asia.

Global warming could melt most Himalayan glaciers by the 2030s, affecting hundreds of millions of people, it says, adding that between 120 million and 1.2 billion people are likely to experience more water shortages by the 2020s.

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