Heavy rain is making it very difficult to get aid to people who need it following the earthquake in south Asia.
New landslides have blocked some roads and helicopters that have been delivering aid are stuck on the ground.
Pakistani Prime Minister Shaukat Aziz says 23,000 people have died in the country, following earlier reports that 33,000 had lost their lives.
The United Nations has asked for $272m (£156m) to help the survivors, and a UK appeal has been launched as well.
A special phoneline has been set up so that the public can donate cash to help the millions affected.
An appeal spokesman said: "Thousands of families are experiencing terrible suffering, particularly children, and we must help in every way we can."
Action Aid, British Red Cross, CAFOD, CARE International, Christian Aid, Concern, Help the Aged, Islamic Relief, Merlin, Oxfam, Save the Children, Tearfund and World Vision are involved in the drive, under the name Disasters Emergency Committee.
The spokesman added: "Many of our agencies are already working in this part of the world, and we are receiving overwhelming evidence that funds are desperately needed for relief work."
Online donation is already possible via the DEC website.
Disasters Emergency Committee
Telephone: 0870 60 60 900
Click on the link on the right of this page to reach the DEC website