"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," it said in a statement.
Cholera is a water-borne disease that causes vomiting and acute diarrhoea, and can rapidly lead to death from dehydration. It spreads fastest in situations with poor sanitation or where contaminated water is used for drinking or for preparing food.
In Zimbabwe, which has the world’s highest inflation rate, many hospitals have shut down and most towns suffer from intermittent water supply, broken sewers and uncollected garbage.
The WHO said stamping out the southern African country’s outbreak would be difficult because of a limited availability of drugs, medical supplies, and health professionals there.
"The start of the rainy season is also of concern," it said.
The United Nations agency and its partners including the International Organisation for Migration (IOM) are distributing emergency health kits, water purification tablets, oral rehydration salts and other essential supplies and training volunteers in hygiene promotion in Zimbabwe’s worst-hit areas.
The number of people being treated for cholera in the northern town of Musina, near South Africa’s border with Zimbabwe, is falling, but the situation remains serious.
"It’s difficult to say the situation is under control, as it is difficult to trace the patients once they are released; we don’t know where they go, we don’t know whether they take risks," John Shiburi, a South African Red Cross Society official in Musina, told IRIN.
According to health workers, nine people are still in hospital in Musina, being treated for cholera-like symptoms. Earlier this week the figure was 14, with the patients apparently all from Zimbabwe, where an epidemic is raging.
The South African government announced on 20 November that it was ready to help Zimbabwe "address the cholera outbreak", and that discussions were underway with the UN World Health Organisation and the regional Southern African Development Community.
The collapse of water and sewerage services in Zimbabwe, worsened by uncollected refuse and the start of the rainy season, have helped the spread of the waterborne disease. Humanitarian officials reported a total of 2,893 people were infected with cholera between the beginning of August and mid-November, with at least 115 deaths.
A hard-hitting South Africa cabinet statement linked Zimbabwe’s cholera crisis to the stalled formation of a government of national unity between President Robert Mugabe and the opposition Movement for Democratic Change, saying the deadlock was exacerbating the country’s humanitarian and economic crisis.
"The reported outbreak of cholera in parts of that country is a clear indication that ordinary Zimbabweans are the true victims of their leaders’ lack of political will and failure to demonstrate seriousness to resolve the political impasse," the statement noted.
Shiburi said that until the emergency in Zimbabwe was resolved, where people were suffering an inflation rate of 231 million percent and shortages of almost every basic item, the flow of Zimbabwean migrants into South Africa would not halt.
An estimated three million Zimbabweans, in a population of less than 12 million, have left the country, many crossing the border into South Africa, the regional economic powerhouse.
"We’ve got two challenges: the outbreak of cholera, and the issue of immigration. That in itself [migration] is a challenge, but the cholera outbreak has worsened the problem. We have [migrants here] who don’t have shelter, who don’t have accommodation," Shiburi noted.
He added that some Zimbabweans arriving without documentation were avoiding Musina and the authorities and "going straight to Jo’burg", South Africa’s economic hub, to look for work.