The UN Children's Fund in Zimbabwe is preparing to deal with a possible 60,000 cholera cases in coming weeks - four times the current official estimates.
UNICEF's Harare chief Roeland Monasch said such a jump could bring the number of deaths to around 3,000.
The United Nations says the outbreak has claimed 575 lives to date, but aid agencies fear the toll could be higher. The capital, Harare, is the worst-hit district with 179 deaths and 6,448 cases as of 4 December.
UK PM Gordon Brown says it is an international crisis and the world must tell Robert Mugabe "enough is enough".
Mr Monasch told the BBC that they were doing all they could to bring mortality rates down.
But he warned that if as many as 60,000 people became infected in the next few weeks, then the cholera epidemic could kill another 2,700.
He says the actual number of people who have already died is probably far higher than official figures as many clinics and hospitals are closed and people in rural areas frequently just bury their dead.
A spokeswoman for the aid agency Oxfam in Johannesburg Caroline Hooper-Box says there's a real danger of the epidemic becoming far worse.
She says by January at least half of the population are going to be without enough food and already Oxfam staff on the ground are saying people are eating only every two to three days.
Ms Hooper-Box says these people are already weakened by extreme hunger and other disease such as HIV and Aids, so when cholera hits it's fatal.
UNICEF has launched an emergency response programme to focus on providing basic services in the short term.
The disease has spread to neighbouring South Africa, Mozambique, Zambia and Botswana.
The situation has forced President Mugabe's government to declare a national emergency and appeal for international assistance.