Flooding, which submerged more than a third of the low-lying and densely populated country in the last two weeks, has killed at least 132 people and affected more than 7.5 million people, disaster ministry officials in Bangladesh said on Wednesday.
"Many flood survivors have lost everything: their homes, their possessions, their crops," the UN World Food Programme's (WFP) Bangladesh country director, Christa Rader, said in a statement.
"People need food right now, and the full impact on longer-term food security threatens to be devastating."
Widespread floods in recent weeks have killed more than 800 people and displaced more than a million in India, Nepal and Bangladesh, with aid workers predicting severe food shortages and water-borne diseases as rains continue to lash the affected areas.
Many families in temporary shelters in northwest Bangladesh are unable to return home and risk hunger and poverty, WFP said.
Seasonal monsoon rains, a lifeline for farmers across South Asia, typically cause loss of life and property every year between July and September, but officials say this year's flooding is the worst in several years.
Crops on more than 10,000 hectares (24,711 acres) of land have been washed away while another 600,000 hectares (1,482,632 acres) of farms have been damaged, the disaster ministry said.
WFP is giving 100,000 elderly and disabled people and households without men Tk 4,000 or $49 a month for three months to buy necessities like food.
($1 = 81.0300 taka)