The top United Nations humanitarian official has stressed the need for a much stronger international and national response to the cholera epidemic in Haiti during a visit to the Caribbean nation.

The UN World Health Organization (WHO) and its regional arm, the Pan-American Health Organization (PAHO), now estimate that based on the speed with which people are being infected, the outbreak that began in late October could affect 400,000 people.

This is considered a worst-case scenario, which is avoidable if the prevention and treatment responses reach people in the poor areas in the capital, Port-au-Prince, and other towns and outlying areas in the country.

"This projection is a wake-up call," Under-Secretary-General for Humanitarian Affairs and Emergency Relief Coordinator Valerie Amos said yesterday in the capital, Port-au-Prince.

"We need to invest in cholera prevention nationwide in Haiti, as well as building more treatment centres and increasing the number of health workers on the ground to support the work already being done," she added.

Ms. Amos saw first-hand some of the humanitarian work already being done in Haiti, which she noted has already saved tens of thousands of lives. "But it is not enough to curb the loss of life, or equip Haitians to tackle this crisis themselves," she said.

"This epidemic has not yet peaked. If we don't respond strongly and quickly enough then more people will die needlessly."

The death toll, as of Monday, stood at 1,200, but the experts have said that the disease – which is spread through contaminated food and water – might have claimed as many as 2,000 people, with some fatalities in remote areas going unreported. The number of reported cases is currently approaching 50,000.

The UN and its partners have appealed for $164 million for additional treatment centres, scaled-up public information campaigns to help people understand how to prevent infection, supplies of medical equipment, rehydration salts, water purification tablets and other essential materials to respond to the outbreak.

As she wrapped up her visit today, Ms. Amos met with President Rene Préval, and visited a displaced people's camp in the Tabarre neighbourhood of Port-au-Prince and a cholera treatment centre. She also met senior leaders from the UN and humanitarian agencies in Haiti, and the non-governmental organization Doctors Without Borders (MSF).