Remote mountainside villages in quake-ravaged Nepal are facing a wait of days before aid workers can assess their needs after landslides and rockfalls cut off access to the outside world.
The death toll is expected to rise "exponentially" when rescuers finally reach the isolated communities, some of which are thought to have been almost wiped out by Saturday's devastating earthquake.
Emergency services and rescuers are said to be exhausted as they continue to work to locate survivors and the dead among the rubble, set up temporary shelters and help the injured.
"The local authorities look absolutely exhausted. They look on the point of collapse," World Vision's Matt Darvas said, speaking to NZME. News Service from Gorkha city, 30km east of the epicentre of Saturday's quake, and 137km northwest of Kathmandu.
"They need reinforcement ... I don't know how they can keep going at this rate, it's completely unsustainable."
World Vision has urged international agencies to focus their efforts on isolated villages which have yet to receive any help on the ground.
Some aid parcels have been dropped close by, but no contact has been made with many of the villages.
"The remote villages that are surrounding me in the mountains and the hills, some of which have been totally destroyed ... are completely inaccessible, even now several days after the quake," Mr Darvas said.
He said Indian military helicopters had been able to drop aid, but were too big to land at the villages.
Mr Darvas spoke of a man he met in Gorkha who could not make contact with his village.
Kumar Gurung, from the remote village of Singla, heard from his "extremely distressed" wife just 30 minutes after the quake. She and their four children, all aged under 16, were in the house eating lunch when the quake struck.
"At the first sign of tremors they rushed from the building and they were safe," Mr Darvas said.
However, it was estimated that 70 per cent of houses in the village - which is home to 750 people - were destroyed.
The village leaders told Mr Gurung that "many, many children and elderly people were trapped underneath the rubble, because those of working age were all out in the fields doing their work".
Reaching the village, which is perched precariously over a cliff on the top of a mountain, would take a seven-day walk - "if it is at all possible to cross the landslides".
Singla is but one of an estimated 1000 villages in the Gorkha region, with 270,000 inhabitants. Mr Darvas said there were many stories of villages facing similar fates.
The death toll was likely to soar once rescuers finally managed to reach villages in the north.
Watch: Drone view of the Nepal quake damage
In Gorkha city, people were sleeping outside on the ground on tarpaulins because everyone was too scared to go inside the buildings, he said.
But no one was getting much rest as aftershocks continued.
On his way to Gorkha, Mr Darvas stopped in Pokhara where he witnessed a number of women giving birth outside on mats in 30C heat because the hospital's maternity ward was full.
Mr Darvas urged people to continue to donate to ensure supplies and resources were delivered to hard-hit areas in the months to come, saying it would take years for the country to rebuild.
Other charities have also been calling for help to deliver urgent life-saving aid.
The Red Cross said it was in a critical phase of the response, when "seconds can mean the difference between life and death".
Unicef was last night sending staff and supplies to the region, aiming to reach almost 3 million children.
A New Zealand urban search and rescue (USAR) team had been due to fly out to Nepal overnight on Monday, but the deployment was cancelled after the Nepalese Government said it had enough USAR capability.
Foreign Minister Murray McCully said the airport in Kathmandu was hugely congested and several supply planes from India had to be turned back.
The USAR team could be sent in future if requested. In the meantime, agencies were working to distribute $1 million in immediate aid from New Zealand.
Meanwhile, a candlelight vigil will be held in Christchurch on Friday in honour of the earthquake victims.
Mayor Lianne Dalziel said it would be an opportunity for Christchurch residents - who knew first-hand the devastation an earthquake could bring - to stand in solidarity with the local Nepalese community.
Nepal Earthquake Appeal
on 0800 90 5000
Unicef: Visit unicef.org.nz/nepal or call 0800 243 575
Oxfam: Visit oxfam.org.nz or call 0800 600 700
Red Cross: Visit redcross.org.nz or call 0800 Red Cross (0800 733 276)
Caritas Aotearoa New Zealand: Visit caritas.org.nz or call 0900 4 11 11
New Zealand Nepal Society: Donations can be made to bank account number 01-0142-0053378-00
Himalayan Trust Rebuild Appeal: Visit givealittle.co.nz/cause/nepalearthquake
TEAR Fund: Visit TEAR fund.org.nz or call 0800 800 777