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STORY: In a camp for people displaced by floods in Nigeria's Borno state, Bintu Amadu is among hundreds of people who have been waiting for hours to see a doctor.

Her son had diarrhea. She says she's been waiting since yesterday, to no avail.

Overwhelmed aid agencies have warned of an outbreak of waterborne disease, amid the region's worst flooding in three decades.

Hundreds of thousands of people, like Amadu, have been forced into displacement camps without food and clean water.

And that's stretching aid agency and government resources, exacerbating a critical humanitarian crisis.

"The demand is so massive. The needs are so massive."

Mathias Goemaere, a field coordinator for Medecins Sans Frontieres, said that Borno residents were already struggling with malnutrition following years of a jihadist insurgency in the region.

And that means their immunity was already suppressed.

"People are living out and about, they are exposed to their environment, so what do we see? A lot of waterborne diseases, diarrhoea, diarrheic diseases, you've got malaria. Malaria is around with a lot of mosquitoes, people are not able to sleep under mosquito nets."

The floods, which have killed more than 30 people in Nigeria, started when a dam burst its walls.

That's after heavy rainfall that has also caused floods in Cameroon, Chad, Mali and Niger.

In the last two weeks of August more than 1.5 million people were displaced across 12 countries in West and Central Africa due to floods.

That's according to the United Nations humanitarian office, which said around 465 people have been killed.

Nigeria's government has separately warned of rising water levels in the country's largest rivers which could cause floods in the oil-producing Niger Delta in the south.