The United Nations says it has yet to reach nearly a quarter of those in need of emergency food aid, 11 days after Typhoon Haiyan devastated the central Philippines.
The World Food Program (WFP) said Tuesday it has so far reached 1.9 million people out of the estimated 2.5 million Filipinos in need of assistance.
WFP executive director Ertharin Cousin told reporters in Manila her agency is not overwhelmed, but faces several logistical challenges in reaching remote areas.
"Every disaster is different. The challenges of the Philippines are primarily geographical challenges, this being an island nation and the logistical challenges of reaching out to different pockets of small communities here."
Thousands of people were killed when Haiyan made landfall, bringing tsunami-like waves and powerful winds that destroyed entire villages.
Initial aid flow was hampered by infrastructure problems, including a lack of electricity, poor communication, impassable roads and little access to fuel.
But aid has begun flowing quicker, thanks in part to a massive relief effort by the United States military, which has about 1,200 soldiers on the ground.
U.S. Navy Commander William Marks said Tuesday many land routes have been cleared, allowing over 80 percent of the aid to be delivered using trucks, rather than by less efficient helicopters.
In a statement, Commander Marks said the development means there is less need for air support from the USS George Washington aircraft carrier that has served as a hub of the helicopter missions. He estimates it will remain in the region for two more days.
The Philippine government says the typhoon killed at least 3,974 people and left about 1,200 missing. Many were swept away and drowned in a huge storm surge triggered by one of the strongest cyclones on record to make landfall anywhere in the world.