The first batch of GlaxoSmithKline's experimental Ebola vaccine has been shipped to West Africa and is expected to arrive in Liberia later on Friday, the British drugmaker said.

The shipment, of an initial 300 vials of the vaccine, will be the first to arrive in one of the three main Ebola-affected African countries, GSK said in a statement.

It will be used in the first large-scale vaccine trials in coming weeks, in which health-care workers helping to care for Ebola patients will be among the first to get it.

Researchers hope eventually to enrol up to 30,000 people in the trial, a third of whom would get GSK's candidate vaccine.

The vaccine, co-developed by the National Institutes of Health in the United States and Okairos, a biotechnology firm acquired by GSK in 2013, is currently being tested in five small phase I safety trials in Britain, the United States, Switzerland and Mali involving around 200 healthy volunteers in total.

"The initial phase I data ... are encouraging and give us confidence to progress to the next phases of clinical testing which will involve the vaccination of thousands of volunteers, including front line health-care workers," said Moncef Slaoui, GSK's Global Vaccines chief.

The vaccine uses a type of chimpanzee cold virus to deliver safe genetic material from the Zaire strain of Ebola, the strain responsible for the unprecedented West African epidemic.

Data so far show "an acceptable safety profile" including in a West African population and across a range of dose levels, GSK said, adding it had now selected the most appropriate dosage for the Liberia trial.

The World Health Organization said on Thursday the Ebola outbreak in West Africa appears to be waning but cautioned against complacency in an epidemic that has seen 21,724 cases reported in nine countries since it started in Guinea a year ago. Some 8,641 people have died, according to WHO data.

Slaoui stressed that GSK's shot, like other candidates from a NewLink Genetics and Merck collaboration, and from Johnson & Johnson and Bavarian Nordic, is still in development and can't be deployed unless and until it proves safe and effective.

"Any potential future use in mass vaccination campaigns will depend on whether the WHO, regulators and other stakeholders are satisfied ... and how quickly large quantities ... can be made," he said.

NewLink Genetics and Merck are collaborating on the vaccine which was originally developed at the National Microbiology Lab in Winnipeg. Trials for that vaccine were temporarily halted in December due to a potential side effect, but were eventually resumed.