Heavy pre-monsoon rainfall and surging upstream flows from India have swollen rivers in northeastern Bangladesh, threatening vast areas with flooding during the crucial summer rice harvest, officials said on Wednesday.

Despite relentless rain, strong winds and thunderstorms, farmers have been rushing to their fields, wading through knee-deep water to cut partially submerged crops in a desperate effort to salvage what they can.

"We're trying to save whatever is still standing," said Mohammad Al Amin, a farmer in Sunamganj, describing the race against rising water levels.

The farmers in the haor (wetland) basin are harvesting ripe Boro paddy, the South Asian country's major rice crop. Significant losses could impact both rural livelihoods and national food supply.

Days of continuous rain, combined with inflows from India’s Meghalaya and Assam regions, have increased the risk of sudden river flooding in vulnerable districts, authorities said.

Fields across Sunamganj, Sylhet, Kishoreganj, Habiganj and Moulvibazar have gone under water in many areas, according to local officials. In several places, floodwaters spilled into cropland after a sudden rush of water weakened or overwhelmed embankments.

Heavy rains have also damaged other crops, including vegetables, raising concerns about potential supply shortages.

The Bangladesh Meteorological Department has forecast further rainfall in the coming days, while officials cautioned that additional upstream flows could increase the likelihood of more widespread flooding across the haor basin.

Agriculture officials warned that even short periods of submergence at this stage could sharply reduce rice yields. Farmers are also grappling with irrigation challenges linked to diesel shortages following disruptions tied to the Iran conflict in the Middle East.

Heavy rain has also caused widespread waterlogging and disruption in major cities, including Dhaka and the port city of Chittagong, where roads have gone under water, slowing traffic, disrupting daily life and adding to pressure on already strained drainage systems.

Bangladesh, one of the world's most climate-vulnerable countries, faces recurrent flood risks. A 2015 analysis by the World Bank Institute estimated that about 3.5 million people are exposed to annual river flooding, with scientists warning that climate change is intensifying such extreme events.

The country, the world's third-largest rice producer, consumes most of its output domestically but often requires imports to cope with shortages caused by floods or droughts.

-Reporting by Ruma Paul; editing by Philippa Fletcher/Reuters