"It's absolutely urgent right now to send tents to give people shelter. If nothing is done there will be thousands of deaths" in mountain villages in the devastated Balakot area, said Thierry Velu, head of the French aid organisation Groupe de Secours Catastrophe Francais.
The group, which has spent four days in Balakot, includes a medical unit working with the Pakistani army that found about 100 serious cases, Velu said on Sunday.
Some survivors who have gone for days without having fractured bones treated have now developed pneumonia and serious infections that will require amputations, he said.
Balakot, Neelum Valley
A Pakistani military doctor also expressed alarm about the health situation in Balakot, a region in North West Frontier Province.
"I don't think that many of the people are going to survive the cold," said the doctor, who identified himself as Bilal. He said the number of lives at risk was in the thousands.
"We've seen cases of diarrhoea, fever and respiratory infections appearing in recent days," he said.
An estimated 3.3 million have
been left homeless in Pakistan
The earthquake, which registered 7.6 on the Richter scale, killed more than 38,000 people in Pakistan and more than 1300 people in India. In Pakistan, more than 3.3 million people have been left homeless.
In another area, the Neelum Valley, Dr Sean Keogh of Britain-based Medical Relief International said on Saturday that several thousand people could die in the next few days if help did not reach their isolated villages.
In remote communities, residents say that even if aid is coming, it is often haphazard and lacking tents, which will be crucial as snow has already fallen on the high mountains.
In the village of Jabori on the foothills of the mountains, the Pakistani army is distributing aid, but villagers say what they sorely need is shelter.
The village in the depths of a scenic valley layered with farmland and pine trees is still partly intact, unlike Balakot, which was almost destroyed.
But also unlike Balakot, the village has not seen the same rush of aid coming from the outside.
"We need tents and food and they gave us mineral water"
Gul Mohammad, 24,
"We didn't have anything, no medicine to care for the injured. We carried them down on stretchers to the hospital and then we waited," Mohammed Sabir, a 60-year-old man, said with resignation in the ruins of his house.
Mohammad Farooq, 21, said his family of 13 had nowhere to go.
"I don't need food. All I need is a tent. It's raining, soon it's going to snow, and people are living outside," he said.
Thousands of people line up for the supplies being handed out by the Pakistani army, but they say it is inadequate.
"We need tents and food and they gave us mineral water," shouted Gul Mohammad, 24, who will go back empty-handed to his hamlet in the more remote mountains.