International peacekeeping troops are consolidating their presence in Haiti after President Jean-Bertrand Aristide fled into exile amid an uprising.
Canadian special forces secured the capital's airport
An advance contingent of about 100 US Marines was followed by French soldiers as military transporters flew into the capital Port-au-Prince.
The city was in chaos after Haitians learned of their president's exit.
But correspondents say the situation now appears calmer and people have started returning to the streets.
Canadian special forces
More countries expected to join later
A group of around 70 men, including the rebel leader Guy Philippe, drove straight through roadblocks in the capital and met no resistance from supporters of the ousted president on Monday.
The BBC's Stephen Gibbs, in Port-au-Prince, says a carnival atmosphere greeted the rebels' arrival.
Mr Philippe's first stop was a police station in the capital. He says he wants to work with Haiti's police force and the international troops to restore security to Haiti.
US Secretary of State Colin Powell says he expects the Americans eventually to number about 1,000 troops.
"I don't think there will be a great deal of fighting, but they have to be prepared for that," Mr Powell told CBS's The Early Show.
Our correspondent says US Marines have already set up a command centre in the airport's VIP lounge.
Several hundred French soldiers were arriving throughout Monday
The first groups of about 50 French soldiers, the US Marines and Canadian forces already on the ground will be followed by reinforcements in a mission backed by the United Nations.
Several hundred French soldiers were expected to arrive in Haiti by Monday night, and Paris has also dispatched a platoon of police officers from a special riot control unit.
Our correspondent says the international troops are entering a lawless city, with some evidence of revenge killings as anti-government rebels clash with supporters of Mr Aristide.
But he says the amateur soldiers roaming the streets are likely to capitulate when faced with professionals from an international force.
Violence flared in the city after Mr Aristide fled the country, with some of the widespread looting and destruction apparently a frustrated response to the ceding of power.
Mr Aristide, his wife and three children arrived in the Central African Republic on Monday. It is not yet clear whether they will stay there or seek asylum in a third country.
Canadian special forces are also at Port-au-Prince airport, where they are helping Canadian nationals who wish to leave Haiti.
US defence officials say the US will take initial command of the multinational force, though that could change once the full UN operation begins.
As well as trying to restore peace in Port-au-Prince, the US Marines will help to deliver humanitarian assistance and repatriate any Haitians caught at sea.
The UN Security Council unanimously authorised a force to stay in Haiti for up to three months to restore security and stability on Sunday night.
It is expected to be followed by a UN stabilisation force, probably including civilian police, which has no time limit.
UN Secretary General Kofi Annan said the international community needed to make a long-term commitment to help Haiti "over the long haul".
All sides in the Haitian conflict have also called for peace.
Rebel leader Guy Philippe, who had been massing his men for an assault on the capital, welcomed the foreign intervention, said: "We just want peace."
Interim leader Boniface Alexandre warned that the future would be difficult.
"Haiti is in crisis... It needs all its sons and daughters. No-one should take justice into their own hands," he urged.
Mr Aristide issues a statement from his temporary shelter in the Central African Republic, criticising the rebels who prompted the crisis by seizing towns and cities across the north in a month-long uprising.
"In overthrowing me, they cut down the tree of peace," he was quoted as saying by the Associated Press news agency.
"But it will grow again, because the roots are well-planted."
The violent protests stemmed from disputed elections in 2000, which the opposition says were rigged.