JOHANNESBURG, South Africa (AP) — Cholera cases in Mozambique among survivors of a devastating cyclone have shot up to 139, officials said, as nearly one million vaccine doses were rushed to the region and health workers desperately tried to improvise treatment space for victims.

Cholera causes acute diarrhoea, 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 the southern African nation now living in squalid conditions in camps, schools or damaged homes.

The Portuguese news agency Lusa quoted Mozambique national health official Ussein Isse for the new toll. 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 some 500,000 people is the hub of cyclone relief efforts.

The World Health Organization (WHO) has warned of a “second disaster” if waterborne diseases like cholera spread in the impoverished nation. It said 900,000 oral cholera vaccines were expected to arrive Monday, and a vaccination campaign will begin late next week.

WHO also has opened seven treatment centres with a total of 400 beds, including 100 in Beira.

“We assume that there are lots of people who will get sick and we want to get prepared,” spokesman Tarik Jasarevic told reporters in Geneva.

Cyclone Idai, which stuck March 14, destroyed more than 50 health care clinics in central Mozambique, complicating the work to contain the disease, Radio Mozambique cited disaster management official Rui Costa as saying.

It is not yet clear whether any cholera deaths have been confirmed.

“We’re not going to test every single case (for cholera) because it’s not difficult to recognise when you look at the diarrhoea of a patient. Once you see it once, you always recognise it,” Gert Verdonck, Doctors Without Borders’ emergency coordinator for Beira, told the AP.

Other suspected cholera cases are outside Beira in the badly hit areas of Buzi, Tica and Nhamathanda, he said, but the chance of spreading in rural areas is smaller because people are more dispersed.

In urban areas, however, cholera “can have a huge impact if not contained quickly”, Verdonck said. He said the 900,000 vaccine doses should be enough to cover targeted areas but that a second dose should be given after two weeks to strengthen protection.