Brazilian troops are leading the mission of 8,000 UN soldiers and civilian police, which are expected to be in place on the island by the end of June.
They are taking over from a multinational force that was dispatched to the island after former president Jean-Bertrand Aristide left in the wake of an armed uprising.
Prime Minister Gerard Latortue sought to reassure the people about the role of the Brazil-led UN force.
“I want to take this opportunity to clearly reaffirm to the Haitian people that this is in no way an occupation of our country. These foreign troops are the concrete and tangible expression of international solidarity with Haiti,” Mr Latortue said.
The BBC?s Stephen Gibbs in Port-au-Prince, says the troops face a daunting task.
While their primary responsibility is to provide security while a transitional government organises new elections, Haitians are expecting them to help the thousands of flood survivors who still depend on aid to survive.
At least 2,000 people are known to have died or disappeared after severe flooding over the past week.
With access routes and roads flooded, aid agencies have been struggling to reach survivors in remote areas with airlifts, using helicopters belonging to US and French troops.
Thousands of survivors in flood-stricken areas are currently dependent on supplies dropped in by helicopter.
More than 100 tonnes of food has been airlifted so far.
And although over the past few days the US-led multinational force has been overseeing the delivery of dozens of jeeps and lorries, no helicopters are expected in the UN equipment.
The BBC correspondent says while the new UN force may be able to help with rebuilding homes, relocating people and helping with aid distribution, it will now be up to aid agencies to organise airlifting missions.
Around 6,700 military officials and 1,622 civilian police officers drawn from 14 nations, are due to join the force, but it‘s unclear if the full number will arrive.
Robert Rothberg, Haiti Analyst at the Kennedy School of Government at Harvard University, told BBC Caribbean Service he was skeptical about the UN?s ability to raise the whole force.
“The UN simultaneously raising forces for Cote d?Ivoire, Congo and conceivably the Sudan… the UN is very fully stretched across the globe. Haiti is unfortunately not the UN?s highest priority,” he said.
Mr Rothberg also said he was unsure about how much the new force can achieve.
“It?s very difficult to put together a force of nine countries, small detachments from across the globe. Few of whom have a direct interest in the Caribbean.”
“The bulk of the US-force are doing a very good job and it?s a great misfortune that they are being pulled out prematurely,” he said.