Cholera cases in Mozambique among survivors of a devastating cyclone have shot up to at least 139, officials said Friday, as nearly 1 million vaccine doses were rushed to the region and health workers desperately tried to improvise treatment space for victims.

Cholera causes acute diarrhea, is spread by contaminated food and water and can kill within hours if not treated. The disease is a major concern for the hundreds of thousands of cyclone survivors in Mozambique, now living in squalid conditions in camps, schools or damaged homes in the southern African nation.

The Portuguese news agency Lusa quoted Mozambique national health official Ussein Isse for the new toll. Mr. Isse declared the outbreak on Wednesday with just five confirmed cases.

Far more cholera cases already were feared. The medical charity Doctors Without Borders told The Associated Press it is seeing around 200 likely cholera cases a day in the Indian Ocean port city of Beira alone. The city of roughly 500,000 people is the hub of cyclone relief efforts.