Nearly 400 Zimbabweans have died from the disease, which has infected more than 9,400 people and spread to neighbouring South Africa and Botswana.
WHO spokeswoman Fadela Chaib said there are very few places where people infected with cholera in Zimbabwe can seek medical care, and the clinics that are open have far too few health workers to contain the outbreak.
"Cholera is only the tip of the iceberg in Zimbabwe. The health system is very weak in this country," she told a news briefing in Geneva.
International aid groups are building latrines, distributing medicines and hygiene kits, delivering truckloads of water, and repairing blocked sewers across Zimbabwe to mitigate the cholera emergency.
The International Committee of the Red Cross (ICRC) has begun delivering food for Zimbabwean doctors, nurses and other health workers who have not been paid because of their country’s economic collapse.
"Some of the staff working in the clinics have not received a salary for weeks, and they cannot keep working if we do not get them food," ICRC spokeswoman Anna Schaaf said.
The agency said on Thursday it was doubling the budget of its Zimbabwe office to nearly 13 million Swiss francs in 2009. "The situation in hospitals is catastrophic," ICRC President Jakob Kellenberger told Reuters.
Zimbabwe’s inflation is more than 230 million percent. Its economic crisis has caused many public hospitals to close, and most towns suffer from only intermittent water supplies, broken sewers, and uncollected garbage.
The U.N. Office for the Coordination of Humanitarian Affairs says that 9,463 people in Zimbabwe have been infected by cholera in the latest outbreak, and that 389 have died.
Cholera spreads through contaminated water used in drinking and food preparation, and poor hygiene. It causes vomiting and diarrhoea and can lead to death from dehydration if untreated.
The U.N. children’s agency UNICEF said that to stop the current outbreak, Zimbawbwe’s water pipes, sewers, and latrines need to be fixed, new boreholes need to be drilled, and water treatment chemicals need to be distributed across the country.
"Without international support, the lives of children in Zimbabwe will remain in grave danger," it said in a statement.