Haitians devastated by Hurricane Matthew looted United Nations trucks shortly before UN Secretary-General Ban Ki-moon arrived for a visit.
The Category 4 hurricane tore through Haiti on 4 October killing about 1,000 people and leaving more than 1.4 million in need of humanitarian aid.
An estimated 175,000 people were made homeless.
The storm also disrupted power, communications and transport links.
"We will mobilise all the resources to help you," Mr Ban told a handful of residents gathered at a local school being used as a shelter for hurricane victims. "Stay strong."
Tensions are high in Les Cayes and elsewhere in Haiti's southwest region because help has yet to reach many families whose crops and water supplies were destroyed, increasing the risk of cholera and malnutrition.
A coordinator for the American wing of the World Health Organisation said the UN base was shut down after looting of two World Food Programme food containers outside the base yesterday.
As Mr Ban approached his car to leave the school amid heavy security, locals shouted, "Our houses were destroyed ... Help us!"
Mr Ban's visit was a chance to improve the UN's standing among Haitians who protested this week against the death of a motorcyclist in an accident they blamed on blue-helmeted peacekeepers.
Mr Ban's final term at the world body expires at the end of the year.
His tenure has been tarnished by a cholera epidemic in Haiti and rape allegations in Central African Republic, both blamed on UN peacekeepers.
Cholera has stalked the regions of Haiti affected by the hurricane, as towns dotting the coastline - many of which had not had the disease in months - have reported spikes in the number of cases and deaths.
Many Haitians lack access to drinkable water after the storm.
Haiti had no documented cholera cases until 2010, months after a 7-magnitude earthquake leveled much of the capital city of Port-au-Prince.
Multiple scientific studies have traced the outbreak to a base in Mirebalais used by Nepalese peacekeepers, about an hour outside of the capital, and the strain of cholera is virtually identical to one endemic in Nepal.
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Meanwhile, the charity Concern Worldwide has described the world's response to the destruction in Haiti a "disgrace".
Concern Worldwide chief executive Dominic MacSorley praised Ireland's support to the devastated people of Haiti to date.
However, he said urged donors around the world to "wake up" and meet the UN's flash appeal for €110m.
Just 20% has so far been donated nearly two weeks after the disaster.
Speaking in Haiti, Mr MacSorley said that nobody should be dying for a lack of money.
"Despite the logistic challenges, this is a country that we have access to.
"There is no war, no bombs dropping and no excuses. The appeal must be met."
"It is a disgrace that there has not been a more robust response, particularly from the big major donors."
