DHAKA, July 19 (Xinhua) -- Flooding sparked by heavy seasonal rains and onrush of water from hills across the Indian borders have seriously affected parts of Bangladesh including central Tangail district, some 97 km away from capital Dhaka.

The flooding has caused major problems for many residents in the district especially where people have also been suffering with erosion of Jamuna, one of the three mighty rivers in Bangladesh.

Floods have caused widespread damage to habitation, crops, roads and highways across vast swathes of the district.

Residents in the district are seen Thursday to leave their houses wading through flooded roads or on boats in search of shelter, or a dry ground to live temporarily.

Md Abu Bakar, an official at the Bangladeshi government's Department of Disaster Management, told Xinhua Monday that the on-going flooding in almost one-third of Bangladesh districts including Tangail has left at least 20 people dead and displaced thousands of families.

According to the official, authorities have rushed teams of disaster response force to carry out rescue operation, distribute relief materials and supervise centers where nearly thousands of families have taken shelter.

Bangladesh Prime Minister Sheikh Hasina has asked officials to remain alert to tackle flood, saying some parts of the country have been flooded and the flood water would slowly come down to the mid areas of the country by the end of August.

Millions of people in Bangladesh, criss-crossed by more than 230 rivers, suffer from flooding as the low-lying country experiences seasonal floods every year.

The International Federation of Red Cross and Red Crescent Societies (IFRC) said on Tuesday that nearly six million people across South Asia including Bangladesh were under threat from rising flood waters following heavy monsoon rains, with more than one million displaced in one Indian state alone.

Quoting the Bangladeshi government's disaster report, leading English newspaper New Age said on Friday that until Wednesday, 3,247,454 people were marooned by flooding in 17 districts.

Over the past week, heavy rains have caused more than 200 landslides in Cox's Bazar, a city in southeastern Bangladesh, forcing about 900,000 people to live in the makeshift camps, IFRC said.

"We are seeing growing numbers of displaced and increasing loss of life with each day of rain. The entire communities have been cut off by rising waters, increasing the risk of people going hungry and getting sick," IFRC Regional Director for Asia Pacific Xavier Castellanos said.

"All of our efforts right now are focused on reaching these people and ensuring that they have the supplies and support needed to withstand coming floods," Castellanos said.