"We are very concerned, and we are planning for all scenarios, including the worst case scenario," WHO's head of emergency response Peter Salama told reporters in Geneva.
WHO has tallied 32 suspected or confirmed cases in the northwestern area of Bikoro, on the shores of Lake Tumbathe near the border with the Republic of Congo, including 18 deaths, between April 4 and May 9.
The cases include three healthcare workers, one of whom has died, Salama said.
The outbreak, declared by the DRC health ministry on Tuesday, is the country's ninth known outbreak of Ebola since 1976, when the deady viral disease was first identified in then-Zaire by a Belgian-led team.
Ebola is one of the world's most notorious diseases, being both highly infectious and extremely lethal.
Salama said the strain raging in Bikoro was the Zaire strain, which also was responsible for the recent west Africa epidemic that killed more than 11,300 people.
He said the affected region of the vast strife-torn central African country is very remote and hard to reach.
This could have a benefit since it could slow down the spread of Ebola, but it also greatly complicates the response.