The agency's staff in the area had reported seeing many families on the road.
"They're coming. You won't find enough space for them here," said Kaghan valley nazim Junaid Qasim at Jaba farm, an organised camp situated between Mansehra and Balakot that can host 6,000 people. "You need at least four to five such camps to accommodate these newcomers."
Javed Ahmad and his family of seven arrived at Jaba camp on Monday with nothing but the clothes on their backs. "We walked for three days from the valley. Fifty more families from our village are also coming," he said.
Sadiq Shah is also new to the camp. After losing his wife and two-year-old daughter in the earthquake, he and his remaining four children were airlifted to Balakot from Paras village in the Kaghan valley.
"There are more than 300 families in my village. Now the road is clear and they will be here in a day or two," said Shah.
Anticipating a possible major influx, UNHCR and other organisations were struggling for the arrangements of additional tents, plastic sheets and Jerry cans at Jaba camp.
A total of 400 UNHCR and Islamic Relief Organisation tents have already been pitched by the Pakistan army and more land is being cleared on the terraces to accommodate the new tents.
Unicef is providing water in tanks and hopes to be able to pipe it in within days. Oxfam is building latrines, while Médecins du Monde is providing healthcare. The International Islamic Relief Organisation is cooking three hot meals a day and building a stove to provide fresh bread for breakfast.
While winter and survival are at the top of people's minds right now, the thought of home is never far away. "I will stay for winter," said Javed Ahmad, a new arrival at Jaba camp. "I have a big house back in the village. If I can get help with building materials, I can repair it and move back in spring."
Meanwhile, UNHCR spokeswoman Jennifer Pagonis, in Geneva, said the first phase of a Nato airlift carrying 860 tonnes of UNHCR aid supplies from the agency's stockpiles in Turkey was completed on Monday.
Nato and UNHCR agreed to launch a second phase of the airlift, which began straight away on Monday night and is set to transfer a further 800 tonnes of UNHCR supplies from emergency stockpiles in Turkey, Jordan and Denmark.
"In the second phase, we'll be delivering another 320,000 blankets, 30,000 mattresses, 1,000 family tents and other materials," Pagonis said.
"About 300 tonnes of supplies in the second phase will come from our stocks in Turkey and the government there has generously agreed to provide trucks and personnel to move it from our warehouse in Iskenderun to Incirlik [airbase]."
On Monday, Norway announced a $1 million donation to UNHCR, bringing the total provided for the agency's earthquake operation so far to $6.7 million. However, UNHCR's immediate needs are for $18 million just to see it through to the end of November.