The appeal was made ahead of a conference of donors in the capital Islamabad on Saturday to raise money to help Pakistan recover in the aftermath of the October 8 quake, which killed nearly 74,000 people and made three million homeless.

UN and Pakistani agencies, the World Bank and the Asian Development Bank estimate the recovery will cost 5.2 billion dollars, only about half of which has been pledged.

"The onset of winter... is likely to result in a second wave of deaths," the International Rescue Committee, Catholic Relief Services, World Vision, Save the Children, CARE International in Pakistan and Mercy Corps said.

"A second disaster is now set to unfold. How many die this time is up to us," they said in a joint statement.

Shelter is the most pressing need, with the first snows already falling in the parts of northern Pakistan affected by the quake.

"The window for responding to the crisis is closing rapidly, but major gaps in funding may leave thousands of families without adequate shelter and resources to survive the winter," the groups said.

"We have the chance to save thousands of lives, but the world community must act now," Mercy Corps' emergency spokeswoman Cassandra Nelson said.

Nelson said the aid groups had the capacity to respond, "but we are under-funded and under-equipped."