The sheer scale of Haiti's quake disaster presented rescuers with a seemingly overwhelming task. Below are some of the main ongoing logistical challenges.
Rescue teams from 17 countries, including France, are on the ground
Port-au-Prince's small international airport has struggled to cope with the number of aid flights arriving in response to the earthquake.
Within days, the Haitian government formally put the airport's operation in US hands and Washington has established a temporary air traffic management system for flights.
The airport has only one runway and standing room for 18 aircraft at a time, so planes arriving with aid have been delayed while those on the ground are unloaded. However, the UN says some 150 aircraft are landing every day.
The US and Canadian military recently contributed equipment to speed up the unloading process but lack of transport and fuel has made it difficult to move goods to other locations.
The main airport in neighbouring Dominican Republic quickly became congested as it supported an alternative route for aid.
But US Southern Command says aid flights have started landing at airfields in Jacmel, southern Haiti, and San Isidro and Barahona airports in the Dominican Republic.
The port has suffered severe damage
The main port in Port-au-Prince was closed after severe damage to the docks and the one major crane at the facility. Some initial aid shipments were diverted to Cap Haitien port.
On 16 January, the first ship finally docked at Port-au-Prince, carrying a cargo of bananas and coal, and the port is now considered functional.
US engineers and dive teams are restoring piers, cranes, and buildings, as well as clearing debris at the port. The UN says the port should be able to receive 350 containers a day as of 25 January, an increase from the present daily capacity of 250 containers.
The port at Jacmel in the south of Haiti is operational for small ships.
Saint Marc and Gonaives ports are reported to be open but their capacity is not yet clear, the UN says.
The US aircraft carrier USS Carl Vinson has arrived off Haiti carrying 19 helicopters. It will serve as a "floating airport" for relief operations.
The US has also sent three amphibious assault ships and several Coast Guard cutters.
Some roads are impassable - either as a direct result of earthquake damage, or because they are blocked by rubble or smashed vehicles. Some aid agencies have been unable to get to their warehouses.
Roads to the neighbouring Dominican Republic, though damaged, are open and the best option for the majority of incoming cargo.
The UN peacekeeping mission (Minustah), which has around 3,000 troops and police in and around Port-au-Prince, is working to clear some of the major roads.
Road access between Port-au-Prince and Leogane - two of the worst affected areas - is reported to be good. But key routes that are open are becoming congested with the movement of people and supplies.
The UN says the security situation is stable with a few reports of scuffles, looting and gunshots. Some rescue crews said they were forced to stop work at nightfall because of security concerns.
Responsibility for maintaining law and order in the capital now rests with the UN mission's international troops and police.
Haiti has no army and its police force has all but collapsed in the aftermath of the earthquake.
UN troops are providing military escort for UN agencies delivering aid and international NGOs have been advised to travel with escorts.
The US, which has sent thousands of troops to help the relief effort, is providing additional capacity at the request of the UN.
Between 500,000 and 700,000 people are believed to have been left homeless as a result of the earthquake, according to the UN's latest estimates.
More than 500 makeshift camps have been identified by the Haitian government, which has requested large tents to set up reception centres for the homeless.
Agencies have assessed 350 sites, which currently accommodate around 472,000 people. However, only six of these sites have access to water sources.
The Haitian government has identified six sites for camps outside of the city, such as land near Croix des Bouquets, and has suggested that these camps should be for 20,000 people each.
Even before the earthquake only half of Haitians had access to clean water. Now most of the remaining water supply been cut off.
Agencies have been working to provide water and sanitation to as many people as possible.
On 20 January, 755,000 litres of water were provided to 151,000 people as well as 7,000 bottles of water to hospitals, orphan centres and a police station. The ICRC is providing clean water for more than 12,000 homeless people living in three camps.
The UN is particularly concerned about the situation in Cite Soleil, one of the capital's poorest neighbourhoods, where there is an acute shortage of water.
Some bottled water is being brought from the Dominican Republic but far more supplies or purification kits are needed.
The USS Carl Vinson, docked off Haiti, is fitted with water-purifying equipment that can make 400,000 US gallons (1.5m litres) of drinking water a day.
Other countries have sent mobile water purification units, which can convert contaminated water from wells and streams into drinking water.
The UN has set up a "Food Aid Cluster" to meet the needs of two million hungry people. The World Food Programme (WFP) has four fully operational distribution sites - in Champs de Mars, Petionville Club and two sites in Delmas and the number of sites is expected to increase.
WFP has provided around three million meals to more than 200,000 people since the start of the emergency response - each person getting a five-day ration. Most were distributed in the Port-au-Prince area, but also in Jacmel, Leogane, Jeremie, Bainet and Gonaives.
The UN says the aim is to distribute 10 million meals over the next week, reaching 100,000 people a day. One thousand metric tons of ready-to-eat meals will arrive in Port-au-Prince on 27 January.
Seven US military helicopters are being used to support aid distributions in areas around the capital.
BURIAL OF THE DEAD
The leading US general in Haiti has said it is a "reasonable assumption" that up to 200,000 people could have died in last Tuesday's earthquake.
Lt Gen Ken Keen said the disaster was of "epic proportions", but it was "too early to know" the full human cost.
The disposal of dead bodies has been a key priority for the relief effort. The bodies of thousands of victims have been piling up in the streets and outside hospitals. Many more remain trapped beneath rubble.
More than 80,000 dead people are reported to have been buried, many of them in mass graves.
The presidential palace, the parliament and many government buildings have collapsed, hampering an already weak central government.
UN Secretary General Ban Ki-moon says the agency is co-ordinating relief work with Haitian President Rene Preval, and that government agencies, including the police services, are now regrouping.
Mr Preval has increased the number of working groups and is designating official group leaders who will liaise with the UN.
An information hub has also been set up at Judicial Police headquarters in Port-au-Prince.
The UN mission has set up an operations centre at the airport to co-ordinate the work of around 26 international search and rescue teams. It says no more urban rescue teams are appropriate at this stage.
Several relief agencies' offices, including the UN's, are damaged and their staff dead or missing. Co-ordination efforts are also being hampered by frequent power cuts and communications outages.
The US naval ship Comfort is a fully-equipped "floating hospital"
UN health specialists say at least eight hospitals or health centres in the capital collapsed or suffered severe damage.
Most public and private hospitals still standing were stretched to the limit in the immediate aftermath, with not enough staff to handle the hundreds of wounded waiting at their gates, the Red Cross said.
Many of the injuries have been appalling. International surgeons have been carrying out an average of about 50 amputations a day.
Field hospitals have been set up by teams from Russia, Israel, Colombia, Jordan and Brazil - including some with resources to perform neurological, orthopaedic, maxial-facial and general surgery.
Helicopters have also been ferrying the wounded to hospitals in nearby countries.
The US hospital ship, USNS Comfort, with 500 medical personnel and 250 beds onboard, arrived in Port-au-Prince harbour on 20 January and has treated more than 230 people.