An ebola outbreak in the Democratic Republic of Congo has killed more than 80 as authorities warned there was no vaccine for the strain in a crisis that the World Health Organization declared an international health emergency on Sunday.

The surge in cases marks the 17th Ebola outbreak in the Congo since 1976.

Some 88 people have died from the highly contagious haemorrhagic fever in the DR Congo, with one death in Uganda, and at least 336 suspected cases.