The World Health Organization said Wednesday the deadly Ebola outbreak in the Democratic Republic of Congo is now an international health emergency after the virus spread this week to a city of 2 million people.

The WHO declared the outbreak a "public health emergency of international concern," a rare designation only used for the gravest epidemics.

"It is time for the world to take notice," WHO chief Tedros Adhanom Ghebreyesus said in a statement, as he accepted the advice of his advisory board to invoke emergency provisions only used by the U.N. health agency four times previously.

A WHO expert committee declined on three previous occasions to advise the United Nations health agency to make the declaration, but other experts say the outbreak has long met the conditions.

More than 1,600 people have died since August in the second deadliest Ebola outbreak in history, which is unfolding in a region described as a war zone.

This week the first Ebola case was confirmed in Goma, a major regional crossroads on the Rwandan border with an international airport. Experts have feared this for months.

A declaration of a global health emergency often brings greater international attention and aid.