The Red Cross warned Thursday that nearly all homes had been wiped out in some towns and villages near the epicentre of Nepal's devastating earthquake.
The International Federation of Red Cross and Red Crescent Societies (IFRC) said they remained "extremely concerned" about the welfare of hundreds of thousands of people in Nepal, five days after a massive earthquake that killed nearly 6,000 people.
In areas outside the Kathmandu Valley, the fate of many people remains unknown, the organisation said.
"Six Red Cross assessment teams are reporting that some towns and villages in the worst-affected districts close to the epicentre have suffered almost total devastation," it said in a statement.
"Local residents are in a desperate situation," it added.
The devastation appeared particularly dire in the Sindupalchowk region, a mountainous area northeast of Kathmandu, which was becoming a major focus of international relief efforts.
"One of our teams that returned from Chautara in Sindupalchowk district reported that 90 percent of the homes are destroyed," said Jagan Chapagain, head of IFRC's Asia Pacific division.
"The hospital has collapsed, and people are digging through the rubble with their hands in the hope that they might find family members who are still alive," he said in a statement.
"We can expect the situation to be the same if not worse in many other places where aid has not yet been delivered," he added.
IFRC said up to 40,000 homes were estimated to have been destroyed in Sindupalchowk, and the World Health Organization said Thursday that some 1,400 people had been killed there.
With so many families in need, the Nepal Red Cross Society said it had almost exhausted its relief stocks which were sufficient for 19,000 families.
Yet getting more aid in through Kathmandu's small international airport is expected to be a challenge, with UN agencies reporting that a number of aid flights have been delayed or turned back due to congestion.
IFRC expects its first two planeloads of fresh aid to arrive at the airport Friday, with stocks to serve 1,000 people and a 60-bed rapid deployment emergency hospital, but warned far more was needed.
In the meantime, Red Cross volunteers have been distributing tarpaulins in affected areas to shelter thousands of people who remain too afraid to return home because of aftershocks and damage to their homes.
The priority now, it said, was moving relief efforts to more remote areas.
"We know what the needs are, and Nepal Red Cross volunteers are ready in every district to distribute relief. The challenge now is bringing sufficient quantities into the country," Chapagain said.