The first confirmed cases of cholera were reported in cyclone-hit Mozambique on Wednesday.

Health authorities and aid agencies had warned of a massive threat of disease in the increasingly squalid conditions following cyclone Idai.

Five cases of cholera were reported in Munhava, a poor neighborhood in the city of Beira, the national director of medical assistance, Ussene Isse, told reporters.

"We did the lab tests and can confirm that these five people tested positive for cholera," Isse said. "It will spread. When you have one case, you have to expect more cases in the community."

Authorities are struggling to provide clean water and sanitation to the city of 500,000 after the March 14 storm. Doctors Without Borders said residents of the city have resorted to drinking stagnant road-side water or water from contaminated wells.

Cholera is a waterborne disease that causes acute diarrhea that can kill in hours if left untreated. It thrives in conditions of poor hygiene and is spread by contaminated food and water.

Hundreds, if not thousands, of people died in the storm and ensuing floods, but the World Health Organization has warned of an impending "second disaster" caused by disease. It said 900,000 doses of oral cholera vaccine would arrive in the next week.

"We were expecting cholera cases and we were prepared for this. We have put all the measures in place to try to mitigate the spread of cholera as much as we can," said Emma Batey, a coordinator at the COSACA emergency aid consortium.

Malaria and typhus both post a major risk to survivors of the storm, as well as food shortages given vast swathes of farmland have been swamped.