“Staff at the outbreak sites see evidence that the numbers of reported cases and deaths vastly underestimate the magnitude of the outbreak,” the organisation said on its website.

“WHO is coordinating a massive scaling up of the international response, marshalling support from individual countries, disease control agencies, agencies within the United Nations system, and others.”

International agencies are looking into emergency food drops and truck convoys to reach hungry people in Liberia and Sierra Leone cordoned off from the outside world to halt the spread of the virus, a top World Bank official said.

In the latest sign of action by West African governments, Guinea has declared a public health emergency and is sending health workers to all affected border points, an official said.