Mass trials of an experimental Ebola vaccine could start in West Africa in December and several hundred thousand doses could be available by the first half of next year, the World Health Organisation has said.

The WHO's assistant director general Marie-Paule Kieny said on Friday that two potential vaccines were undergoing clinical trials. Larger trials in West Africa could begin in December if those tests proved effective.

"All is being put in place to start efficacy tests in the affected countries as early as December," she said at the agency's headquarters in Geneva.

"Before the end of first half of 2015 we could have available a few hundred thousand doses. That could be 200,000 - it could be less or could be more.

"Vaccine is not the magic bullet but when ready, it may be a good part of the effort to turn the tide of the epidemic."

She said that the organsation had held talks on Thursday with medical experts, officials from affected nations, pharmaceutical firms and funding agencies about the trials.

The candidates currently undergoing clinical trials are the Canadian-made rVSV, and ChAd3, which is made by British firm GlaxoSmithKline. There are five other potential vaccines that will be tested next year, Kieny said.

More than 4,800 people have died in West Africa of Ebola. Guinea, Liberia and Sierra Leone are the worst affected countries.

Nigeria and Senegal were declared free of the disease last week after no new cases were reported for 42 days - twice the virus's maximum incubation period.

Hoever, Mali recorded its first case on Friday, and a total of 42 people who were in contact with the sufferer have been isolated.

The disease continues to alarm countries outside of West Africa, with the US on Thursday confirming a New York doctor had contracted the virus while working for the medical charity, Doctors Without Borders in Guinea.