Floods in southwest Bangladesh have inundated vast swathes of farmland, affecting nearly a million people, many of whom are stranded on embankments with no food or shelter, officials said Tuesday.

Heavy monsoon rains in recent days have caused at least five rivers to burst their banks, flooding more than 1,000 square kilometres (400 square miles) of farmland in the remote Satkhira district.

"Nearly a million people have been affected by floods in Satkhira. Among them, 120,000 people have been displaced," district administrator M. Abdus Samad said.

The government has stepped up relief efforts in the area, Samad said, adding that those who have lost their homes are staying in a network of 284 temporary relief centres and are receiving emergency rations.

More than 1,500 tonnes of rice and a large quantity of high-energy biscuits have been distributed by government workers to the displaced families, he said.

The World Food Programme (WFP) is also providing emergency food assistance to 57,000 people affected by floods in Satkhira, the agency said in a statement.

"A vast number of ultra-poor people are stranded on embankments, with no access to food and shelter," said Michael Dunford, the acting WFP Country Director.

Bangladesh is criss-crossed by more than 200 rivers and is regularly hit by floods during the monsoon season, spanning from June through September.

The country receives some 80 percent of its annual rainfall during the monsoon, when heavy rain water gushes from two Himalayan rivers -- the Ganges and the Brahmaputra -- causing many local rivers to breach their banks.

Last month, 21 people were killed and 400,000 were marooned in flash floods and landslides in southeastern Bangladesh.

In 2007, during the most recent episode of severe flooding, nearly 1,100 were killed and more than 2.5 million were displaced.