The United Nations estimated last week that the storm killed about 500 people in Mozambique, about 250 in Zimbabwe, and about 60 in Malawi. Whole villages with thousands of residents were flooded, so more bodies may yet be found.

Cholera, usually transmitted in contaminated water , is rapidly spreading. The Mozambique government said Tuesday that it had recorded more than 1,000 cases, including one death.

Aid officials privately called that an underestimate, saying treatment centers are seeing hundreds of cases each day. Some victims are already dead when they are carried in.

The disease drains the body of fluids and electrolytes. If cholera victims reach help in time, they can almost always be saved with rapid rehydration and one dose of antibiotic.

Nine treatment centers with about 500 beds offering intravenous rehydration have been set up, eight of them run by Doctors Without Borders and one by the International Red Cross Federation.

Short-term centers with oral rehydration for ambulatory patients have also been created.

“If the epidemic continues the way it is now, that should be enough,” said Dr. Gilles van Cutsem, an H.I.V. specialist with Doctors Without Borders helping out in the crisis. “If cases massively increase, we’ll have to increase capacity.”

The aid group has hired 80 local doctors and nurses, and trained them to treat cholera, he said.

The Mozambique health ministry and aid agencies are collaborating on a campaign using radio and local health workers to tell people to seek help at the first sign of diarrhea and to be vaccinated against cholera.