China is "vulnerable" to the deadly Ebola outbreak due to the soaring number of Chinese working in Africa and poor infection control at home, a co-discoverer of the virus warned Thursday.

Belgian microbiologist Peter Piot also said experience with other viral outbreaks showed that airport screening was largely ineffective, and repeated his earlier criticism of the World Health Organization's initially "slow" response to the crisis.

China is Africa's largest trading partner and Beijing's diplomatic footprint across the continent has expanded hugely in recent years as it seeks resources to drive the world's number-two economy.

"Thousands and thousands of Chinese workers and people are in Africa now," Piot told an Ebola-focused seminar in Tokyo.

"So it is not impossible that one of them will go (back) to China. I am more concerned about that than about Africans going to China."

The quality of care at Chinese public hospitals was another concern, he added.

"I don't think you can really stop people from travelling, so these patients will show up in any country in the world, but China I thought is quite vulnerable," Piot said.

Responding to questions earlier this week about what China was doing to prevent an epidemic at home, foreign ministry spokesman Hong Lei said: "We have enhanced the screening of body temperatures of those entering China and made epidemic prevention preparations.

"So far, owing to our effective work, no suspected case has been reported in China. But we will remain on high alert and will never let down our guard."

The Ebola outbreak ravaging west Africa has claimed 4,922 lives, according to the latest WHO update, with the vast majority of deaths in Liberia, Guinea and Sierra Leone.

Piot said that toll was more than three times the number of people who have died from Ebola over the past four decades.

- Airport screening 'doesn't work' -

The scientist, who co-discovered the virus in 1976 in Zaire, now known as the Democratic Republic of the Congo, called on countries to focus on containing the outbreak in west Africa, rather than largely-ineffective airport screening.

"In today's globalised world, even if there is an epidemic thousands of thousands of miles from home, everybody of the world is at risk," he said.

"We have seen important cases in Spain and the United States -- this is kind of really unavoidable. The only way to prevent it is not closing borders and also screening passengers -- that really doesn't work -- but it is to stop the epidemic there in west Africa.

"Many countries including the UK have started screening passengers coming from west Africa for fever and so on. Frankly, from a scientific perspective, it's not very effective."

Piot, director of the London School of Hygiene and Tropical Medicine, added that the WHO, the UN's health agency, could have done a better job in responding to the outbreak earlier this year.

"WHO has been slow in responding particularly in the regional office of Africa, which should be the strongest of the regional offices. They should have been the front-line in responding and they did not do that job," he said.

The WHO said in its latest update that the rate of new Ebola infections appears to be slowing in hard-hit Liberia, although the crisis was far from over.

Piot said his "optimistic scenario" would see the epidemic start slowing by Christmas.

But he also called for vigilance "until the last person has died or survived without having infected somebody, because one person is enough to refuel, reignite an epidemic".