West Africa's Ebola epidemic is an "extraordinary event" and now constitutes an international health risk, the World Health Organization (WHO) said on Friday.
The Geneva-based U.N. health agency said the possible consequences of a further international spread of the outbreak, which has killed almost 1,000 people in four West African countries, were "particularly serious" in view of the virulence of the virus.
"A coordinated international response is deemed essential to stop and reverse the international spread of Ebola," the WHO said in a statement after a two-day meeting of its emergency committee on Ebola.
The declaration of an international emergency will have the effect of raising the level of vigilance on the virus.
"The outbreak is moving faster than we can control it," the WHO's director-general Margaret Chan told reporters on a telephone briefing from the WHO's Geneva headquarters.