Most of the tents given to survivors of the South Asia earthquake in October are not designed for winter conditions, a leading aid agency says.
The biggest threat to survivors is now the cold
The International Organisation for Migration (IOM) says the issue of shelter "is becoming more critical".
About three million people lost their homes in the quake which Pakistan says left some 73,000 dead.
The IOM is leading the operation to distribute emergency shelter to the survivors of the disaster.
Relief organisations have long been appealing for 'winterised' tents designed to withstand the cold of a Himalayan winter.
The IOM is working alongside the United Nations and other organisations in the earthquake zone.
IOM spokesman Darren Boisvert said he had earlier believed that three-quarters of the tents given out were not winterised.
But on Friday he told journalists in the Pakistani capital, Islamabad: "The latest is that 90% of tents are not winterised.
Heavy duty tent designed for long-term use by a single family
PVC groundsheet sewn onto the sides for wind proofing and to retain warmth
Some types are designed to accommodate cooking stoves
ICRC estimates that 30,000 such tents are required in Pakistan
"Winterised tents are expensive, they are hard to procure and must be shipped from overseas."
But the UN official with overall responsibility for the relief effort said that did not mean that the non-winterised tents were not adequate.
Jan Vandemoortele said people could still use blankets and tarpaulins to provide extra protection.
"When we say that 90% of tents are not winterised, it does not mean that they are inadequate, the proportion of tents that is not adequate is much, much smaller," he said.
Mr Vandemoortele warned that "the situation remains very difficult. We are on a knife's edge."
He said the biggest problems for relief workers were not the cold conditions but "complacency and pessimism".
'Sticking to plans'
Nato troops have been making a substantial contribution to the relief efforts.
However, Pakistan said on Thursday that it would not be asking Nato to extend its commitment once its initial mission expires.
"We are sticking to our plans," a foreign ministry spokeswoman said.
Nato says an exact date for its troops to withdraw will be decided next week. Reports suggest it will be in January or February.
International donors have pledged some $5.4bn (£3.14bn) to help Pakistan recover from the earthquake, the government says.
Many of the pledges are in the form of low interest loans.
The authorities in Indian-administered Kashmir say some 1,400 people there were killed by the earthquake.