Floods and mudslides in northeastern Brazil have killed around 40 people, left hundreds of thousands homeless and devastated swathes of farmland.

Unusually heavy rain has been falling in the region for more than two months, and forecasters expect it to continue. The flooding - said to be the worst in recent memory - has washed out bridges and roads, submerged homes and destroyed crops, according to aid workers.

Aid agencies say there are fears of food shortages and growing risks of outbreaks of water-borne diseases and insect infestations.

Those worst affected are farmers living along the Amazon River who have seen their livelihoods wiped out, reports the Adventist Development and Relief Agency (ADRA).

Aid group Plan says rivers in the state of Maranhao, where most people live on less than $2 a day, have risen as much as 15 metres above average levels, and the government response has been insufficient.

The agency says 57 municipalities have already declared a state of emergency. In some areas, classes have been suspended so that schools can serve as shelters. People lack drinking water, food, clothes, mattresses and other basics.

In the town of Bacabal in Maranhao, the BBC reports that the flooding has washed bodies out of the cemetery and killed many animals, yet some people have been drinking the water. Residents are also refusing to leave their homes, partly because of fears of looting.

Brazil's President Luiz Inacio Lula da Silva has been quoted as saying the floods in the north and a drought in the south of the country are signs of climate change.

"Brazil is feeling climate changes that are happening in the world, when there is severe drought in areas that don't have drought, when it rains too much in places where it doesn't rain," the BBC reported him saying.

Early estimates put the economic damage at at least $500 million, but that figure doesn't include agricultural losses that have not yet been fully assessed, according to Inter Press Service (IPS).

The news agency reports that heavy rains were forecast as far back as January and says the crisis reveals a lack of public investment in disaster prevention.

Lula has blamed state and municipal governments for failing to take steps like preventing the construction of houses along rivers, according to IPS. For their part, local authorities have complained about central government delays in releasing funds for disaster prevention work.

Ercilia Torres, a geographer the University of Brasilia, told IPS it was a combination of both factors. "The need for these funds is only remembered when tragedies happen; later it's forgotten," she said.

AlertNet has a gallery of images from the flooded region.

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