The Ebola outbreak that has claimed more than 1,000 lives in West Africa is moving faster than aid organisations can handle, the medical charity MSF said on Friday.

The warning came a day after the World Health Organization (WHO) said the scale of the epidemic had been vastly underestimated and that "extraordinary measures" were needed to contain the killer disease.

The UN health agency said the death toll from the worst outbreak of the disease in four decades had now climbed to 1,069 in the four afflicted countries, Guinea, Liberia, Nigeria and Sierra Leone.

"It is deteriorating faster, and moving faster, than we can respond to," MSF (Doctors Without Borders) chief Joanne Liu told reporters in Geneva, saying it could take six months to get the upper hand.

"It is like wartime," she said a day after returning from the region where she met political leaders and visited clinics.

WHO said on Thursday it was coordinating "a massive scaling up of the international response" to the epidemic.

"Staff at the outbreak sites see evidence that the numbers of reported cases and deaths vastly underestimate the magnitude of the outbreak," it said.

The latest epidemic erupted in the forested zone straddling the borders of Guinea, Sierra Leone and Liberia, and later spread to Nigeria.

WHO declared a global health emergency last week -- far too late, according to MSF, which months ago warned that the outbreak was out of control.

Liu said while Guinea was the initial epicentre of the disease, the pace there has slowed, with concerns now focused on the other countries.

"If we don't stabilise Liberia, we'll never stabilise the region," Liu said.

Concerns have also centred on the Nigerian cases, which are in Lagos, sub-Saharan Africa's largest city.

"Right now we have no past experience with in urban setting," said Liu.

No cure or vaccine is currently available for Ebola, which the WHO has declared a global public health emergency.

It has also authorised the use of largely untested treatments in efforts to combat the disease.

Hard-hit nations are awaiting consignments of up to 1,000 doses of the barely tested drug ZMapp from the United States, which has raised hopes of saving hundreds.

Canada says between 800 and 1,000 doses of a vaccine called VSV-EBOV, which has shown promise in animal research but never been tested on humans, would also be distributed through the WHO.

MSF's Liu warned against focusing on drugs.

"In the short term, they're not going to help that much, because we don't have many drugs available. We need to a get a reality check on how this could impact the curve of the epidemic," she said.

The last days of an Ebola victim can be grim, characterised by agonising muscular pain, vomiting, diarrhoea and catastrophic haemorrhaging described as "bleeding out" as vital organs break down.

Although the WHO confirmed that other African countries, including Kenya, were labelled "high risk" due to their popular transport hubs, it also emphasised that air travel, even from Ebola-affected countries, is low risk because the virus is not airborne.