Two Ebola-related deaths have been confirmed in a displacement camp in eastern Congo, the UN refugee agency said, with aid workers warning the risk of the disease spreading quickly in crowded refugee sites was high and worrying.

The two victims were internally displaced people living in the Kpangba camp, which hosts 30 000 refugees, the UNHCR said in the report published on Thursday.

The virus has now spread across three provinces since the WHO declared the outbreak a public health emergency of international concern on May 17.

The three provinces - Ituri, South Kivu and North Kivu - have been devastated by decades of conflict and house over 5-million displaced people.

An aid worker told Reuters that the two victims were a mother and daughter who died on May 31 and June 1, and who were tested for Ebola by the World Health Organisation after they died.

"It’s a highly populated area so the risks of transmission are obviously higher and worrying," the source said. "These are tents with tarp walls, where do you isolate if you have symptoms?"

Aid workers describe cramped conditions at the camps with poor hygiene facilities, with sometimes hundreds of people sharing a toilet and open defecation.

"We are all really worried that Ebola in these camps will spread extremely quickly and that there will be panic and people will flee all over whether or not they're contacts, whether or not they're ill," Caitlin Brady, interim country director for the Danish Refugee Council in Congo, told Reuters.

As of Friday, Congo reported 676 confirmed ⁠cases and 136 deaths in an outbreak that ​has also spread to neighbouring Uganda, which has reported 19 cases.

The outbreak involves the rare Bundibugyo strain of Ebola, for which ​there is ​no approved ⁠treatment or vaccine.

The disease went undetected for weeks and first responders say they are playing catch-up.