(CNN) -- A cholera epidemic in northern Nigeria has killed more than 350 people since June and threatens to spread to the entire country, according to the west African nation's health ministry.
The outbreak had sickened more than 6,400 people and killed 352 people by Wednesday, the federal Ministry of Health reported. Cholera occurs in much of the country under normal conditions, but the lack of clean drinking water, and recent flooding following heavy rains are fueling the spread of disease, the ministry reported.
"Although most of the outbreaks occurred in the northwest and northeast zones, epidemiological evidence indicates that the entire country is at risk," the ministry reported.
Two-thirds of rural Nigerians lack access to safe drinking water, and fewer than 40 percent of the people in the affected states have access "to toilet facilities of any description," the health ministry said.
The intestinal infection causes diarrhea and vomiting that can cause severe dehydration without prompt attention, according to the World Health Organization.
As 120,000 people die each year from cholera, and the disease can kill within hours if untreated, the WHO says.
Nigeria's announcement follows reports earlier this week that another cholera outbreak in neighboring Cameroon had killed nearly 300 people by earlier this week.
The outbreak began in May and has exceeded 3,000 cases, said Dr. Eric Mintz, the leader of the Centers for Disease Control and Prevention's global water sanitation and hygiene epidemiology team.