With more rain predicted, relief workers are scrambling to bring medicine, water purification tablets and dried food to people trapped in their homes or moved to camps, the Health Ministry said.
At least 70,000 people were evacuated to flood shelters after the rain-swollen Gumti River breached parts of a mud levee earlier this month, inundating more than 200 villages in eastern Comilla district. The flooding affected more than 600,000 people and destroyed rice crops.
Another 300,000 people were hit in the country's northern and western regions, Dhaka's Flood Forecast and Warning Center said.
The cracks in the 100-mile Gumti embankment widened Thursday as more rain fell in the rice-growing region, 55 miles east of Dhaka. Authorities fear what the future may hold.
Two other mud levees collapsed Wednesday in Kurigram district, 150 miles north of Dhaka, under pressure from the swollen Dharla River.
Up to 3.6 inches of rain worsened the floods in six northern districts. Low-lying areas around the capital, Dhaka, also were flooded.
Bangladesh, a delta nation of 125 million people, has 230 rivers running down the Himalayas into the Bay of Bengal.
Last year floods swamped two-thirds of the country and caused $2 billion in damage to crops and infrastructure.