The World Health Organization (WHO) has extended its global emergency designation for the Ebola outbreak in the Democratic Republic of the Congo but said the sharp decline in cases was "extremely positive".

"As long as there is a single case of Ebola in an area as insecure and unstable as eastern DRC, the potential remains for a much larger epidemic," WHO Director-General Tedros Adhanom Ghebreyesus told journalists in Geneva on Wednesday.

Tedros expressed hope that the emergency could be lifted within the next three months on the advice of the WHO's emergency committee of international experts.

The WHO last July declared the Ebola outbreak a "public health emergency of international concern" - a designation that gives the UN health agency greater powers to restrict travel and boost funding.

Tedros on Tuesday said only three cases had been reported in the past week in the DRC.

But for the epidemic to be declared over, there have to be no new cases reported for 42 days - double the incubation period.

The health emergency designation last year came a few days after a patient was diagnosed with the virus in the provincial capital Goma, the first case in a major urban hub.

More than a month before that, the WHO reported that the virus had spread to Uganda for the first time.

The recent outbreak was first identified in August 2018 and has since killed more than 2,300 people in eastern DRC - an area where several militia groups are operating.

This is the second-worst outbreak of the disease since 2014, when it killed about 11,000 people, mostly in Guinea, Liberia and Sierra Leone.

Efforts to contain the current outbreak have been hindered by attacks on health workers and conflicts in the east.