There are not enough warm tents in the world to protect refugees from the South Asia earthquake from the coming winter, a top UN official has warned.
Only the heaviest tents will protect against the brutal Kashmiri winter
Andrew Macleod told the BBC that the emergency was so vast it was an even bigger challenge than the 2004 tsunami.
He said the problem was growing every day, and was "outside the scope of any government to handle".
The warning came amid a dispute between Pakistan and India over an Indian offer of helicopters to aid relief work.
Pakistan said it would accept the Indian army aircraft, but not their pilots or crew.
India responded that it would not be possible to provide military helicopters without Indian pilots and crew.
The BBC's Aamer Ahmed Khan in Karachi says an agreement between the historic rivals could potentially double the size of the fleet of relief helicopters operating in Pakistan and Pakistan-administered Kashmir.
Good weather has allowed helicopter relief efforts to resume, but 20% of the areas worst-hit may still not have been reached.
Nine days after the earthquake hit Kashmir and parts of Pakistan, India and Afghanistan, at least two million people are still homeless and at the mercy of the weather, aid officials warn.
Mr Macleod, operations manager of the UN Emergency Response Team working out of Islamabad, the Pakistani capital, said winter-weight tents were needed to protect people from the "cold and brutal winter" to come.
But he warned: "The need here is greater than the existence of tents in the world. We need more tents than exist."
Death toll grows
Deaths in Pakistani-run Kashmir alone may exceed 40,000, local officials say.
Sikander Hayat Khan, the regional prime minister, said he believed that up to 70,000 had also been injured.
If confirmed, the new death figures would bring the total to 54,000 in all areas affected by the quake.
Helicopter crews are making hazardous trips into the mountains
Pakistan's government puts the overall number of deaths in Pakistan-administered Kashmir and North West Frontier Province at about 40,000.
In Indian-administered Kashmir, officials say 1,400 people were killed.
Aid workers say more are bound to die unless either they reach shelter, or shelter reaches them.
Mr Macleod said while many refugees were converging on centres like Islamabad and Rawalpindi, many others could not make such a journey, over several mountain ranges, when roads had been blocked or swept away in landslides.
He said the relief operation was "mobilising every possible resource" to reach such people, "from massive helicopters to feet", and including mules.
But he said the challenge was bigger than after the 2003 earthquake in Bam, Iran, or even the 2004 tsunami.
"Here we've got over 15,000 villages spread out through the affected region," he told the BBC's Newshour radio programme.
"The affected areas are much larger in geographical size than the tsunami, and rather than being in flat coastal areas, we are operating in some of the highest mountains and deepest valleys in the world."
From first light on Monday, under clear skies, helicopters were flying in and out of Muzaffarabad, in Pakistani-administered Kashmir, once again after two days of disruption due to storms at the weekend, the BBC's Mike Wooldridge reports.
More and more people are being discovered with untreated injuries sustained in the earthquake and, increasingly, their wounds are becoming infected and gangrenous, our correspondent says.
"We saw rows of people in a really bad way with suppurating wounds," Sean Keogh, a doctor with British medical aid group Merlin, told Reuters news agency after a three-day trek in the badly-hit Neelum valley.
"There are 1,000 to 2,000 significantly wounded that need surgical treatment. Wounds are pouring pus, patients are going to get septic and die."
Continuing rain and snow in Indian-administered Kashmir was still hampering relief efforts there on Monday, the Associated Press reported.
* Many roads in the affected area are damaged and/or impassable