Threats of freezing temperatures and unusually heavy snowfall in hard-to-reach elevations are adding to concerns over huge financial shortfalls.
A meeting in Geneva earlier this week that sought to boost the waning international response brought pledges of only $16 million. The United Nations said the cost of responding to the earthquake could reach $550 million, an increase from earlier estimates of $312 million.
The U.N. Office for the Coordination of Humanitarian Affairs said it had only $117.4 million, or 23 percent, of the funding from the international community sought by the United Nations to provide food and shelter to survivors.
The response "is not enough," said OCHA spokeswoman Elizabeth Byrs. "We need money immediately to be able to reach people now, not in two to three months because people will be dead by then."
An OCHA statement estimated that as many as 200,000 people in the mountains have not received any assistance, warning there is only about a three-week window to reach survivors before snow closes off paths into the valleys.
The U.N. World Food Programme also said it had sharply increased its estimate of the number of people in need of aid to 2.3 million, of whom less than a fifth had been reached so far.
The WFP had only received 16 percent of the needed $56 million.
Survivors remain in desperate need of food and medical care after millions were left homeless from a massive earthquake that killed 55,000. Aid officials worry that a sluggish response could produce a second wave of deaths from starvation and a lack of shelter.
Reaching survivors trapped at high elevations has proven to be a logistical challenge because many mountain roads were swept away or have been blocked by landslides triggered by the quake.