Aid agencies fighting a cholera epidemic in Haiti say they are suffering a severe shortage of trained medical personnel and supplies.

The United Nations says at least 100 extra doctors and 1,000 nurses are needed and has appealed for volunteers.

The outbreak has killed more than 1,500 people in five weeks and the death toll is reported to be climbing by dozens each day.

The outbreak has sent 27,933 people into hospitals for treatment in just over a month.

To date, 140 have died of the virulent diarrheal disease in the destroyed capital of Port-au-Prince, where more than 1m people are living in sprawling tent cities since a January earthquake.

Officials fear the disease could spread quickly because residents have little access to proper sanitation.

Health officials say hundreds of thousands of Haitians are likely to catch the disease and the epidemic could last a year.

UN Under-Secretary-General for Humanitarian Affairs Valerie Amos said it is crucial that the outbreak be brought under control.

'We have to control the outbreak and we have to bring down the percentage of people who are dying and we have to do that as a matter of urgency,' Ms Amos said.

'If untreated, cholera, a virulent diarrheal disease, can kill in hours, but if caught early enough can be easily treated through re-hydration of the infected person.

'I'm being told it hasn't reached its peak yet, that it will get worse before it gets better,' Ms Amos added.

Much of Haiti's health infrastructure was shattered by the 12 January earthquake, which killed more than 250,000 people.

Ms Amos said it would take time to solve Haiti's huge problems, stressing that even before the earthquake and the cholera epidemic the country's health and development levels were among the lowest in the world.

'This kind of an assumption that when there is a disaster, you can fix it in two or three months, it just isn't true,' she added.

Meanwhile, the head of UN forces in Haiti today vowed that a weekend presidential vote will proceed in a 'calm, peaceful climate, without violence'.