The Ebola virus outbreak in West Africa is racing ahead of efforts to control it and at least $600 million is needed to get the unprecedented epidemic under control, UN health officials said Wednesday.

"This Ebola epidemic is the largest, most severe and most complex we have ever seen in the nearly 40-year history of this disease," Xinhua quoted Director-General of World Health Organisation (WHO) Margaret Chan as saying here.

The outbreaks are racing ahead of the control efforts in West African countries, Chan said.

The WHO chief noted that there have been about 3,500 confirmed or probable Ebola cases and more than 1,900 deaths from the deadly disease.

David Nabarro, Senior United Nations System Coordinator for Ebola, estimated that at least $600 million is needed to get the necessary support to the countries to get the outbreak under control.

Nabarro warned of "a serious economic downturn" in the affected West African nations as a result of Ebola outbreak, which would complicate international efforts to contain the disease.

The WHO officials said they were working with commercial airlines to bring their services back to Ebola-stricken countries as cancellation of flights were hurting international efforts to contain the outbreak.

Chan also emphasised that it is uncalled for to refer to Ebola epidemic as an "African disease", warning that this stigmatisation makes the coordinated global response much more difficult.