South Asia's earthquake was more devastating than last year's Indian Ocean tsunami in terms of the number of homeless and destruction to infrastructure, a UN official said.
Hussein Gezairy, who heads the World Health Organisation's Cairo-based regional office that covers Pakistan, said it would be "much, much more difficult" to reach quake victims in the Himalayas than the tsunami survivors.
"In the tsunami 1.5 million people were made homeless, but in this case we expect more than 2.5 million to be homeless.
"For the 1.5 million people who were homeless something like 10 billion dollars were mobilised. I do not expect this to be happening in Pakistan, but I hope that people will give much more."
The death toll was far higher in the tsunami. Some 217,000 people were killed when giant waves battered 11 Indian Ocean countries on December 26.
The earthquake on the weekend of October 8 and 9 measured 7.6 on the Richter scale and killed more than 25,000 people in Pakistan and 1,300 in India.
It has also left 2.5 million people homeless and destroyed entire towns across an area of 20,000 square kilometres.
It has become the biggest disaster in Pakistan's history.
Mr Gezairy said it would be far more difficult to reach earthquake victims still cut off in the mountains.
"The tsunami was all along the coasts, no roads or bridges were destroyed and the damage was a few hundred metres inside," he said.
"During the tsunami it was possible to have some ships and in this case only helicopters can reach the disaster areas, but they cannot transport a large number people and equipment.
"It is much, much more difficult than the tsunami."
Quake-hit Pakistan is in a "desperate situation" with survivors outside major towns still cut off five days after the disaster, UN relief chief Jan Egeland says.Mr Egeland has taken a helicopter tour of the disaster zone in Pakistan-administered Kashmir.
"This is a desperate situation. As you can see we are making progress in the more populated areas but it is so hard to reach the others," Mr Egeland said.
"We're still racing against the clock and we need to get more helicopters, more water, more tents and more money."
Local and international agencies are struggling to cope with the scale of the devastation in a mountainous and already impoverished region on the edge of the Himalayas.
Editor: APD, with material from news agency AFP.
