By Michelle Nichols

UNITED NATIONS (Reuters) - A "massive response" is needed to help Haiti in the wake of Hurricane Matthew and the United Nations is mobilizing on all fronts to help get the recovery under way, U.N. Secretary-General Ban Ki-moon said on Monday.

"Some towns and villages have been almost wiped off the map," Ban told reporters. "Tensions are already mounting as people await help. A massive response is required. U.N. teams are working with local officials to assess needs."

The United Nations appealed for $119 million on Monday to bring life-saving assistance to 750,000 people in southwestern Haiti, which is reeling from a direct hit by Hurricane Matthew.

The money will go to provide food, drinking water and shelter to the most vulnerable among 1.4 million people in need, after large areas of crops were destroyed and infrastructure was damaged, the U.N. said in the three-month appeal to donors.

"Tensions are already mounting as people await help. A massive response is required. U.N. teams are working with local officials to assess needs," Ban said.

The powerful hurricane, the fiercest Caribbean storm in nearly a decade, slammed into Haiti last Tuesday with 145 mile-per-hour (233 kph) winds and torrential rains. A Reuters tally of numbers from local officials showed about 1,000 people were killed.

Cholera has also killed at least a dozen people following the storm. Cholera causes severe diarrhea and can kill within hours if untreated. It is spread through contaminated water and has a short incubation period, which leads to rapid outbreaks.

Cholera was accidentally introduced to Haiti by U.N. peacekeepers, who dumped sewage into a river after the 2010 earthquake. The outbreak has since infected hundreds of thousands of people and killed more than 9,000.

The U.N. has not legally accepted responsibility for the outbreak, but Ban has said he regrets it and that the world body has a "moral responsibility" to help. He is due to present a new response to cholera in Haiti this month.

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"I am developing a new approach to the cholera situation and this will encompass support for people affected by the disease and for efforts to build sound water, sanitation and health systems in order to help eliminate cholera in Haiti," he said.

"This disaster makes it even more vital to significantly step up our support - and to do so right now," Ban said.

(Reporting by Michelle Nichols; Editing by Chizu Nomiyama and Tom Brown)