The UN's Food and Agriculture Organisation (FAO) said more than one million people were at high risk of infection in the absence of safe drinking water.
More than 70 per cent of springs, irrigation canals and rivers around the country have dried up.
Eric Laroche, the assistant director-general of the WHO, has called for drastic action to be taken over the cholera outbreak.
Laroche warned the outbreak would continue unless "political differences are put aside," impoverished Zimbabwean health workers are paid, and the country's health system is bolstered.
In one area of the country visited by an Al Jazeera correspondent, state morgues have stopped functioning and communities were burying bodies that had been lying there for more than a year.
Bright Matonga, Zimbabwe's deputy information minister, said the bodies were not those of cholera vicitms.
"The report that you have just aired refers to bodies that were not collected from the mortuary since January 2008, [and] there was no cholera at that time," he told Al Jazeera on Tuesday.
|Bodies have been lying in mortuaries without anyone claiming them for burial [EPA]
"We had a cholera outbreak. It was very intense at the end of last year. We called for help and the help came from the World Health Organisation and other NGOs. Really the situation now has improved vastly.
"We are able to quickly detect, quickly prevent, quickly educate people. We are on top of the situation although you can never say it is under control. "
Paul Garwood, a WHO spokesman, told Al Jazeera "we are in the middle of a major outbreak and we are seeing increasing cases".
"On most days the outbreak is on a national scale with cases being recorded in eight of the country's 10 provinces," he said.
"It's not yet under control. There are intensive efforts to try and bring it under control. It must be realised that this is an extraordinary outbreak - a public health emergency - and an extraordinary response is required."
Overloaded medical services have also been hit after health workers went on strike to demand higher wages.
Zimbabwe suffers the second-worst maternal mortality rate in the world after Sierra Leone with about 130 out of every 1,000 babies dying shortly after birth, experts say.
Hyperinflation and a downward-spiralling economy have added to the humanitarian disaster.
With an official inflation rate of 231 trillion, the Zimbabwean dollar has been rendered practically worthless, leading to severe shortages of food and foreign exchange.
Zimbabwe's central bank devalued its dollar on Monday by 12 zeros, turning one trillion dollars into one dollar, and issuing seven new notes in an attempt to counter the economic degradation.
The crisis also comes amid a backdrop of political deadlock.
Robert Mugabe, the president, and Morgan Tsvangirai, the opposition leader, are just beginning to agree on a power-sharing deal after disputed elections in March last year.
The sticking point has been the distribution of key ministerial positions within the government between Mugabe's Zanu-PF and Tsvangirai's Movement for Democratic Change.