HARARE (Reuters) - Zimbabwe's health minister has warned that a cholera outbreak which has killed more than 400 people could spread in the rainy season running to April.

The World Health Organisation (WHO) says the epidemic sweeping the southern African state is only the tip of a major health crisis, and on Friday put the cholera death toll at around 400 and nearly 10,000 infection cases.

Health Minister David Parirenyatwa told the state Sunday Mail newspaper that 425 people have died of the disease.

"What I am afraid of is that now that the rain season has come, all faeces lying in the bushes will be washed into shallow wells and contaminate the water," he was quoted as saying.

"Management of water and sanitation is primary to the cholera problem," Parirenyatwa added.

Some local rights groups estimate that up to 1,000 people may have died from the water-borne disease since August as many communities have no clean water.

WHO said on Friday a lack of clean drinking water and adequate toilets were the main triggers for Zimbabwe's epidemic, a diarrhoeal disease that is especially fatal for children.

The UN agency 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.

International aid groups are building latrines, distributing medicine and hygiene kits, delivering truckloads of water, and repairing blocked sewers across Zimbabwe to combat the outbreak, which has moved into South Africa and Botswana.

On Saturday, Harare City Council announced that it had decided to offer free graves for cholera victims as residents are already under pressure from an economic crisis, including shortages of food and banknotes.

The chairman of a rights association of Zimbabwean medical doctors told a private Sunday Standard newspaper that based on the government's own statistics, they estimate that cholera has killed at least 800 people in the last four months.

"Determining the exact number of people who have died from cholera could be very difficult because of the information blackout that characterised the early days of the epidemic," Douglas Gwatidzo said.

"But with what we have the deaths cannot be anything less than 800 and I believe we are fast approaching 1,000," he said.