The Disasters Emergency Committee is to launch a major television appeal over the Ebola crisis, the first time it has called for donations in response to a disease.
The committee, which is made up of 13 of the UK's major aid charities, said it took the decision because the killer virus threatens to become a "catastrophe".
The DEC described the spread of the virus as "explosive", and said it was devastating communities, health services and people's ability to support themselves.
Ebola, which has killed almost 5,000 people and infected more than 13,000, has hit Liberia, Sierra Leone and Guinea the hardest.
The DEC said some parts of West Africa faced catastrophe within 60 days unless urgent help was provided.
The UK's main broadcasters, including Sky News, are due to screen the appeal tomorrow.
DEC chief executive Saleh Saeed said: "This appeal is completely unprecedented and that is a sign of just how serious the situation in West Africa has become.
"In its 50 year history the DEC has launched appeals for humanitarian disasters caused by floods, famines, earthquake, typhoons, and countless conflicts.
"We have never run an appeal in response to a disease outbreak - until today.
"While many chronic diseases cause untold suffering in poorer countries, the worst acute outbreaks of deadly diseases such as measles or cholera have usually occurred in the wake of another type of disaster.
"In West Africa today we are seeing a disease create not just a medical crisis but a humanitarian emergency.
"Without urgent action to stop the spread of Ebola and to help those affected by the crisis, parts of West Africa face catastrophe within 60 days."
DEC members, including the British Red Cross, Oxfam and World Vision, have already been involved in helping dispose of victims' bodies, running treatment centres and providing food to families.
The BBC, ITV, Channel 4, Channel 5 and Sky will carry the appeal, the DEC said, with support from the committee's major partners including ITN, BT, Post Office, British Bankers Association, Royal Mail, RadioCentre and NewsNow.
Ahead of the appeal, the World Health Organisation said there had now been 13,703 Ebola cases in eight countries and revealed the spread of the virus may be slowing down in Liberia.
The organisation's assistant director General Bruce Aylward said: "Do we feel confident that the response is now getting an upper hand on the virus? Yes, we are seeing slowing rate of new cases, very definitely."
But he said he would be "terrified" if people interpreted his statement as meaning the disease was under control, adding: "It's like saying your pet tiger is under control."
He said if current trends continued, the worst hit countries - Guinea, Liberia and Sierra Leone - should be able to "comfortably" meet a target to scale up Ebola containment measures by 1 December.
In the US, Defence Secretary Chuck Hagel ordered all troops returning from Ebola missions in West Africa to be kept in supervised isolation for 21 days.
More than 1,000 US troops are in Liberia and Senegal supporting efforts to combat the virus.
:: To make a donation visit www.dec.org.uk, call the 24 hour hotline on 0370 60 60 900 or donate £5 by texting the word SUPPORT to 70000.