Operations were under way today to evacuate 400,000 refugees from Haiti's earthquake-shattered capital into tented villages in the suburbs and surrounding countryside.
Public buses were dispatched to collect survivors from around the city and shift them out of the disaster zone to organised encampments, where food distribution, sanitation services and hospital facilities can be better co-ordinated.
It was the first decisive step towards managing Haiti's refugee crisis in which at least half a million displaced residents have been left sleeping in makeshift street shelters erected among the debris.
The US, anxious to prevent a water-borne exodus of refugees from Haiti to Florida, has begun preparing a 1,000-bed tented camp at the Guantanamo Bay naval base on the southeastern tip of Cuba.
It will be used to hold Haitians who may attempt to flee their homeland by sea, and has enough tents in store to accommodate a further 10,000, according to Rear-Admiral Thomas Copeman, of the US Navy.
However as the homeless of Port-au-Prince were being rounded up, it remained unclear what awaited them, with officials saying that so far they had identified sites that would hold 10,000 people at a time but little evidence that proper facilities had yet been established there.
"The government has made available to people free transportation. A large operation is taking place.
"We're in the process of relocating homeless people," Paul Antoine Bien-Aime, Haiti's interior minister, said.
An initial 100,000 people would be sent to tented settlements near the Port-au-Prince suburb of Croix-des-Bouquets, with more to be set up elsewhere for another 300,000.
A fleet of 34 buses roamed Port-au-Prince picking up residents.
Using cardboard, plastic sheeting and materials plucked from the ruins, survivors have improvised nearly 450 temporary settlements in the city, according to the International Organisation for Migration, relying on 330 food distribution points and 80 water trucks for daily rations.
The facility being prepared for unwelcome migrants at Guantanamo stands on the opposite side of the military base to the US-run terrorist detention centre that, under a deadline set by US President Barack Obama, was to have been closed down by today.
Human-smugglers charging $5,000 (€3,500) a trip have operated for years between Haiti's north coast and Florida, 700 miles away, dropping illegal migrants on beaches or tipping them into the water and fleeing when the US Coast Guard gives chase.
Coast guard officials said there were no indications that a mass migration was under way.
However they were ready to enforce the 2004 national Migration Plan that instructs such agencies to "deter, dissuade or disrupt" any surge of illegals towards US shores.
The Jesuit Refugee Service -- a Catholic organisation providing on-the-ground emergency relief to about 16,000 Haitians -- said that calls from some quarters to open up Guantanamo to refugees on a wider basis, to provide emergency shelter, would not be a favourable option.
"Such a drastic action should be undertaken as a last resort," said Christian Fuchs, communications director for the Washington-based group.