Nearly a week after an earthquake devastated Haiti, emergency supplies of food, water and medicine are beginning to reach large numbers of survivors.
But the security situation in the capital Port-au-Prince is feared to be deteriorating and doctors are now worried about the spread of disease.
Medical teams pouring in to set up mobile hospitals say they are already overwhelmed by the casualties and warn of immediate threats from tetanus and gangrene, as well as the spread of measles, meningitis and other infections.
No-one has begun to estimate the number of injuries from the magnitude 7.0 earthquake, which destroyed much of the capital, Port-au-Prince. Haitian officials continue to say the death toll is likely to be between 100,000 and 200,000.
The World Food Programme says it is now feeding 100,000 people, but security remains a major challenge. Gang violence has reportedly broken out in several parts of the devastated city as armed police try to stop looters. Trucks delivering aid are being given military escorts.
One of the leading private security companies operating in Haiti, Page Security says that with the country's main prison in ruins, ciminal gangs intend to exploit the crisis to the maximum.
US Navy helicopters have dropped 14,000 emergency food parcels and 15,000 litres of water into a secure area near Port-au-Prince. Officials are now deciding whether to use the air drops throughout the country.
People are continuing to flee the capital, with many seeking United States visas. The BBC reports that as many as 5000 people have lined up outside the American embassy, desperate to join relatives among the large Haitian-American community in the US.
US troops arrive
US media is reporting that more than 2200 US marines have arrived off the coast of Haiti aboard the amphibious ship USS Bataan. They are equipped with heavy lifting and earthmoving equipment, a dozen helicopters and medical support facilities.
In New York, the UN Secretary General, Ban Ki Moon, says he wants the Security Council to authorise the deployment of another 3500 police and soldiers to Haiti.
Mr Ban says the key priorities are unclogging the bottlenecks hindering the delivery of aid, and coordinating the international response to help survivors of last week's earthquake.