At least 20 people have died and more than 5.2 million have been affected in Bangladesh by floods caused by relentless monsoon rains and overflowing rivers, officials said on Sunday.

The floodwaters have left many people isolated and in urgent need of food, clean water, medicine, and dry clothes, particularly in remote areas where blocked roads have hampered rescue and relief efforts.

Government Chief Adviser Mohammad Yunus said in a televised address that the administration has adopted all necessary measures to ensure a swift return to normality for flood victims.

Yunus, a Nobel Peace Prize winner, is leading the interim government that was sworn in after former Prime Minister Sheikh Hasina fled the country following a student-led uprising this month.

Abdul Halim, a 65-year-old farmer from a village in the Comilla district, said his mud hut was swept away by a 10-foot-high surge of floodwater in the middle of the night.

"There are no goods and no water. Barely anyone has come with the relief (aid) deep inside the villages. You have to physically go close to the main road to collect it," he told Reuters television.

Some people in Bangladesh have alleged that the floods were caused by the opening of dam sluice gates in neighbouring India, an assertion New Delhi has rejected.

"We have begun discussions with neighbouring countries to prevent future flood situations," Yunus said.

The Bangladesh Meteorological Department has warned that flood conditions could persist if the monsoon rains continue, as water levels are receding very slowly.

More than 400,000 people have taken refuge in around 3,500 shelters in the 11 flood-hit districts, where nearly 750 medical teams are on the ground to provide treatment, with the army, air force, navy, and Border Guard Bangladesh assisting in rescue operations, authorities said.

An analysis in 2015 by the World Bank Institute estimated that 3.5 million people in Bangladesh, one of the world's most climate-vulnerable countries, were at risk of annual river flooding. Scientists attribute the exacerbation of such catastrophic events to climate change.

"The impact of this year's monsoon rains has been widespread and devastating," said Kabita Bose, Country Director of Plan International Bangladesh.

"Entire communities have been completely inundated, and there are now millions of people, including children, in need of safe shelter and lifesaving humanitarian assistance," she said. 

(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)