The death toll in the region more than doubled in the last five days, despite heavy rains beginning to wane and water levels receding in some of the worst-affected areas.
Downpours and overflowing rivers over the past fortnight have swamped vast swathes of eastern India, where officials on Monday said 102 people had died in Bihar state.
At least 120 are missing and feared dead following severe floods and landslides in mostly mountainous Nepal, authorities said, while flash foods floods killed 23 people Pakistan last week.
Torrential rains in Bangladesh have killed more than 47 people in the last two weeks, with at least 700,000 others forced to flee their homes.
Rain-swollen rivers have broken through at least four embankments, submerging dozens of villages, in one of the worst floods to hit the country in years.
Heavy rains and overflowing rivers have swamped 23 districts in northern and northwestern Bangladesh, and five more are at the risk of being flooded as water levels in two rivers are still rising, the country’s Water Development Board said.
The government has opened more than 1,000 temporary shelters but many people are unable to reach them and authorities are struggling to deliver relief supplies to those who are marooned.
“We have enough relief materials but the main problem is to reach out to the people,” Foyez Ahmed, deputy commissioner of Bangladesh’s Bogra district, said. “We don’t have adequate transport facilities to move to the areas that are deep under water.”
Monsoon rains soak South Asia between June and October every year, often causing flooding, but the intensity of the deluge in Bangladesh is uncommon.
In India’s tea-growing state of Assam, close to the border of Bangladesh, severe flooding has displaced millions of people and killed more than 60.
Separately, at least 32 people were killed on Sunday in lightning strikes in Uttar Pradesh, India’s most populous state in the north.
India’s weather office on Monday forecast “extremely heavy” rain in four of the 14 districts of the southern state of Kerala.
Kerala last year faced its worst floods in about a century, with heavy rain and landslides killing nearly 500 people, destroying houses and wiping out farmlands.
Monsoon rains, which deliver 75 per cent of India’s annual rain, have not been evenly distributed.
The Himalayan region has received substantially more rain than some of the areas in the plains, where there has been 60 per cent less rain than the average for previous years, according to the state-run India Meteorological Department.