Nearly 300 people have died in Zimbabwe in recent weeks in a cholera outbreak which has hit about 6,000 people, the World Health Organization reports.
The UN body predicted the water-borne disease would continue to spread because of poor sanitation in the impoverished country's urban areas.
Many hospitals have shut down and most towns suffer from poor water supply, broken sewers and uncollected waste.
An outbreak of cholera on this scale is rare in Zimbabwe, correspondents say.
While the disease is endemic in Zimbabwe, it seems this will be the worst outbreak since 2000, Michel Van Herp of the aid agency Medecins Sans Frontieres (MSF) told the BBC.
The WHO said that tackling the problem would be difficult because of the local shortage of drugs, medical supplies and health professionals, and the start of the rainy season was "also of concern".
"The outbreak is likely to continue as the water and sanitation situation is worsening, with severe shortages of potable water, sewage and waste disposal problems reported in most of the populated areas," a WHO statement said.
In Geneva, the UN Office for the Coordination of Humanitarian Affairs specified that cholera had spread to all of Zimbabwe's provinces.
It and the WHO put the total number of suspected cholera as of 18 November at 6,072 with 294 deaths, BBC reported.