A force of US marines was scheduled to arrive last night, with a French contingent of between 120 and 140 troops due to join them this morning.
In New York, the UN security council convened at the request of the US and France to discuss sending a multinational force to restore order in the troubled country.
China's UN envoy, Wang Guangya, the security council president for February, predicted quick action. "It seems that this is a common feeling that something should be done by the council and that action is needed to restore law and order," he told reporters.
George Bush, the US president, ordered the deployment of marines to prevent either pro-Aristide gangs, or the rebel forces encircling them, from gaining control. It was unclear how many US troops would be sent, although the broadcaster CNN put the number at several hundred. Other reports put the figure as high as 2,000 marines on three warships. The American contingent is intended to serve as the vanguard of an international force.
Guy Philippe, the former police chief who led the revolt against Mr Aristide, welcomed news of the imminent arrival of the marines and said his troops would not fight any more. "If we move in Port-au-Prince it will be [for] security but we don't intend to fight any more. Time is up for fighting," Mr Philippe said from Cap-Haitien in Haiti.
By early afternoon, men claiming to be members of Mr Philippe's National Resistance Front had been seen in several suburbs of the capital.
In the main square of one suburb, Petionville, unarmed civilians looted the police station until armed residents of the area drove them away. "We are civilians trying to help restore order," said one of the residents.
Inspector Michel Lucious, of the Haitian police, was at the looted police station and would not say whether the police were now working with the rebels.
President Bush said the fact that Mr Aristide had fled Haiti early yesterday morning meant that "the constitution is working". He added: "There is an interim president. I have ordered the deployment of marines as the leading element of an international, interim force to help bring order and stability to Haiti.
"It is essential that Haiti has a hopeful future. This is the beginning of a new chapter in the country's history.
"I would urge the people of Haiti to reject violence, to give this break from the past a chance to work. The United States is prepared to help."
The US has been criticised for failing to move quickly enough to defuse the situation and for not producing a viable alternative to Mr Aristide, who resigned under pressure from Washington.
"My resignation will avoid a bloodbath," Mr Aristide said in a written announcement. "Haiti's constitution should not drown in the blood of the Haitian people."
After leaving Port-au-Prince, Mr Aristide went to the neighbouring Dominican Republic, then flew to Antigua, where his plane refuelled. Antiguan officials said he was flying on to South Africa. Pretoria denied any contact with Mr Aristide, but a US state department official said an unnamed African country had agreed to grant him asylum. Panama had also agreed to offer him temporary refuge.
Meanwhile, Yvon Neptune, who will temporarily remain as prime minister, called for calm and said: "I know it is not what the vast majority of the people of Haiti wished to have happened."
Mr Bush repeatedly stressed that the White House was working within the international community, a likely attempt to deflect any criticisms of unilateralism in the wake of the Iraq war.
A state department spokesman also stressed that the American troops were being sent to Haiti at the invitation of the country's interim president, Haiti's chief justice, Boniface Alexandre.
"The wild card here is the rebels. Are they with the programme?" a state department official told Reuters. "We want to make sure we neutralise them. Not necessarily by going after them but the timely insertion of some kind of deterrent is important."
For the people of Port-au-Prince, however, the situation remained desperate. As plumes of smoke were seen rising near the presidential palace, gangs who had terrorised opponents of Mr Aristide and had vowed to defend the capital from a rebel assault massed on the streets of the city centre, firing their weapons and attacking petrol stations and banks.
The men opened fire on at least one car filled with journalists, and the mob was heard to shout: "International press, terrorists!"
Unconfirmed reports said the jails had been opened and prisoners freed.
The uprising, sparked by fear and frustration with Mr Aristide's government, has so far claimed at least 100 lives.