Two Dutch doctors feared to have contracted the deadly Ebola virus while working in Sierra Leone are set to be flown back to the Netherlands "as soon as possible", the foreign ministry said Saturday.

The healthcare workers could be back home by Sunday afternoon "if all goes well", spokesman Harald Wychgel from the Dutch Institute for Public Health and the Environment (RIVM) told AFP.

The two men are not yet showing any symptoms of the , he added.

Doctors Nick Zwinkels and Erdi Huizenga, who were working at the Lion Heart Medical Centre in the western town of Yele, "came into contact with three people who then died from the Ebola virus", according to spokesman Friso Wijnen.

"They will be repatriated to the Netherlands as soon as possible," he told AFP.

The clinic mostly treats cases of malaria.

Zwinkels said he and his colleague came into contact with the Ebola patients last week. "I can still sleep but I am very worried," the 31-year-old told Dutch public broadcaster NOS.

The two doctors will be flown out on a special flight and immediately transferred to an isolation unit in a hospital in the western city of Leiden. Tests will then be carried out to determine whether they have contracted the tropical virus.

The World Health Organization said on Friday that the current Ebola outbreak in west Africa, the worst ever, had killed more than 2,400 people. Sierra Leone, Liberia and Guinea are the hardest-hit countries.

Also on Saturday, French development secretary Annick Girardin pledged nine million euros ($11.5 million) towards combatting Ebola in Guinea, including through the construction of a new treatment centre.

Speaking in the Guinean capital Conakry, Girardin, who stressed she was the first minister from Europe to visit any of the Ebola-struck nations, said: "Under no circumstances must Guinea and the other countries affected by the virus remain isolated."

Ebola can cause fever, vomiting, diarrhoea, organ failure and internal and external bleeding.

The only spreads among people in close contact with the bodily fluids of those infected, and most developed nations can sufficiently isolate the sick in order to ward off Ebola's spread.