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.
Zimbabwe's own government has reported fewer deaths, putting the figure at 90, but Health Minister David Parirenyatwa said this week that his ministry was "battling to control unprecedented... outbreaks".
He identified Budiriro, a suburb of the capital Harare, as "the epicentre of the disease", adding that the current wave of cholera had begun in September in Chitungwiza, a satellite town south of Harare.
Admitting the situation in government hospitals was "bad", he told the Herald newspaper he hoped food would soon be made available under the Reserve Bank's programme to ensure Zimbabweans had basic commodities.
The country's Association of Doctors for Human Rights highlighted the dire state of a health service once widely admired in Africa.
"Our health delivery system, previously the envy of many developing countries, is now teetering on the verge of virtual collapse," it said.
"Sick people in need of medical attention are being turned away from Zimbabwe's hospitals and clinics."
Harare's Central Hospital officially closed down last week and now hardly a doctor or nurse is in sight, Zimbabwean journalist Brian Hungwe reports from the city.
Cholera-sufferers would be "coming to hospital to die because there is nobody to care for anyone", said Dr Malvern Nyamutora, vice-chairman of the Junior Doctors' Association.
"Cholera is treatable, just fluids and tetracycline [an anti-biotic] is enough, but if you get people dying of this diarrhoea - that explains the state of the health crisis," he added.