Monsoon rains have caused widespread flooding in northeastern Bangladesh and India, stranding nearly 6 million people and killing at least 41 people.

The flooding in Bangladesh, described by a government expert as potentially the country’s worst since 2004, was exacerbated by the runoff from heavy rain across Indian mountains.

“Much of the country’s northeast is under water and the situation is getting worse as heavy downpour continues,” said Mohammad Mosharraf Hossain, chief administrator of Bangladesh’s Sylhet region.

Before this week’s rains, the Sylhet region was still recovering from what was then its worst flooding in nearly two decades late last month, when at least 10 people were killed and four million others were affected.

Seasonal monsoon rains, a lifeline for farmers across South Asia, also typically cause deaths and property damage every year.

Bangladesh and India have experienced increasing extreme weather in recent years, causing large-scale damage. Environmentalists warn climate change could lead to more disasters, especially in low-lying and densely populated Bangladesh.

Bangladesh’s Sunamganj district – the worst hit – is nearly cut off from the rest of the country, Hossain said, adding that authorities and the army were focused on rescuing trapped people and distributing relief.

Many of Bangladesh’s rivers have risen to dangerous levels, said Arifuzzaman Bhuiyan, head of the state-run Flood Forecasting and Warning Centre.

In neighbouring India’s northeastern state of Assam, armed forces were called in for rescue efforts after landslides killed at least nine people and displaced nearly 2 million from their homes in the last 10 days, officials said.

“Soldiers are helping police and civil authorities in several parts of Assam in evacuating trapped villagers,” Jogen Mohan, the state’s revenue minister, told Reuters.

Torrential rains lashed 25 of the state’s 33 districts for a sixth day.