ABUJA, Aug. 23 (Xinhua) -- Four people have been confirmed killed in the latest cholera outbreak in Nigeria's northeastern state of Adamawa, said an international humanitarian agency on Friday.

A total number of 633 cases have been reported in three local government areas affected by the outbreak as of August 16, the Norwegian Refugees Council (NRC), a humanitarian agency providing aids to refugees and internally displaced persons (IDPs) in the northeast region of Nigeria, said in a statement.

Those affected by the outbreak are mostly IDPs. Due to recent heavy rains and flooding, more cases could be confirmed over the coming weeks, said the humanitarian agency.

Cholera is a highly virulent disease characterized in its most severe form by a sudden onset of acute watery diarrhea that can lead to death.

The Adamawa state government has officially declared an outbreak of cholera in the three local government areas during the rainy season.

"Displaced people are living in sub-human conditions across the region," said the NRC which also noted there are no sanitation or drainage facilities in most IDPs camps.

"People are going to the toilet in open spaces because there are no facilities for them to use and now that the camps are filled with stagnant floodwater, water-borne diseases like cholera quickly spread," it added.

Last year, at least 97 people were confirmed killed by a cholera outbreak in Nigeria's northeast region during the rainy season.