"This will go to support to UN agencies to meet emergency needs that include . . . food, water, medication, but also logistical support," said Jens Laerke, spokesman for the UN humanitarian agency OCHA.
A UN flash fundraising appeal to donors will also be launched in coming days, he told reporters in Geneva.
"This is a race against time. It is also a race against a moving target, in the sense that we also do not have a full assessment of the needs and the requirements in the rural areas outside of Kathmandu," he said.
UN humanitarian chief Valerie Amos has appointed OCHA's resident coordinator in Nepal, James McGoldrick, to oversee the coordination of the relief response, Laerke said.
The massive 7.8-magnitude quake on Saturday was the Himalayan nation's deadliest disaster in more than 80 years, killing over 5,000 people and causing massive destruction.
More than 100 people died in neighbouring countries such as India and China.
Over 10,000 people have been injured while the UN estimates eight million people have been affected, including 1.3 million children in urgent need of humanitarian aid.
In Nepal, there are fears the death toll could jump once rescuers discover the full extent of devastation in villages outside Kathmandu.
Aid flights turned away
Rick Brennan, head of the World Health Organization's Emergency Risk Management unit, voiced particular concern about rapidly reaching people with life-threatening wounds, like head and spinal injuries, and "what we call crush syndrome."
Hospitals have been overwhelmed, with morgues overflowing and medics working flat out to cope with an endless stream of victims suffering trauma or multiple fractures.
Brennan told reporters the five major hospitals in Kathmandu were still functioning, although some had been damaged, but that WHO feared hospitals in other districts may have suffered worse damage.
Humanitarian agencies said Monday they were preparing a massive aid operation to the country, such as flying in planeloads full of food, medical supplies, tents and blankets.
But they are facing significant logistical problems, including congestion, as well as difficult weather and landing conditions at the Kathmandu airport.
"There have been many flights (carrying aid) on the way to Kathmandu that have been forced to return, simply because there was no way they could land," Laerke said.
The World Food Programme said it had a plane loaded and ready in Dubai, which had not yet been able to leave due to overcrowding at the airport in Nepal.
Inside the country too, getting aid out to where it is needed is a challenge, WFP spokeswoman Elisabeth Byrs said.
"Roads are impassable because we fear more landslides and rockslides," she told reporters, adding that the agency was planning to try to use helicopters and small planes to get aid to more remote areas.
WFP said it planned to provide food assistance to some 1.4 million people in the country in acute need of food over the next three months.
Norway announced on Tuesday that it will give €15.5 million euros to the relief efforts in Nepal, making it one of the largest contributors so far to the disaster response.