Fears that the west African Ebola outbreak could spread to other continents has grown with European and Asian countries on alert and a leading medical charity warning the epidemic is out of control.
Doctors Without Borders (MSF) said the crisis gripping Guinea, Liberia and Sierra Leone would only get worse and warned there was no overarching strategy to handle the world's worst outbreak of the disease.
The US Peace Corps announced on Wednesday it was pulling hundreds of volunteers from the three countries.
And another US group, Christian charity Samaritan's Purse, was also temporarily withdrawing its non-essential staff from Liberia, citing regional "instability and ongoing security issues".
Hong Kong announced quarantine measures for suspected cases, although one woman arriving from Africa with possible symptoms tested negative, while the EU said it was ready to deal with the threat.
The International Civil Aviation Organisation (ICAO) has held talks with global health officials on potential measures to halt the spread of the disease.
In Britain, Foreign Secretary Philip Hammond chaired the government's COBRA crisis management committee to assess the situation. One person has tested negative for the disease.
"The prime minister does regard it as a very serious threat," Hammond said. "We are very much focused on it as a new and emerging threat which we need to deal with."
He said the emergency meeting had decided that the best approach was to provide "additional resources to deal with the disease at source" in west Africa.
Ebola can kill victims within days, causing severe fever and muscle pain, vomiting, diarrhoea and, in some cases, organ failure and unstoppable bleeding.
Since March, there have been 1201 cases of Ebola and 672 deaths in Guinea, Liberia and Sierra Leone, according to the World Health Organisation (WHO).
The European Union is equipped and ready to treat victims should the deadly virus be found in its 28 member states, an EU source said in Brussels.
"We cannot rule out the possibility that an infected person arrives in Europe but the EU has the means to track and contain any outbreak rapidly," the source said.
The isolation and negative testing of a suspected case in Valencia in Spain showed that the "system worked", added the source.
"The level of contamination on the ground is extremely worrying and we need to scale up our action before many more lives are lost," said EU Humanitarian Aid Commissioner Kristalina Georgieva.
In Hong Kong, a densely populated city previously scarred by disease outbreaks such as the 2003 SARS epidemic, health officials confirmed they would quarantine as a precautionary measure any visitors from Guinea, Sierra Leone and Liberia who showed fever symptoms.
One woman arriving in the southern Chinese city from Africa, who showed symptoms including fever and vomiting, has tested negative for Ebola.
Bart Janssens, MSF's director of operations, warned that governments and global bodies had no "overarching view" or vision of how to tackle the outbreak.
"This epidemic is unprecedented, absolutely out of control and the situation can only get worse, because it is still spreading, above all in Liberia and Sierra Leone, in some very important hotspots," he said.
"If the situation does not improve fairly quickly, there is a real risk of new countries being affected," he told La Libre Belgique newspaper.
A British doctor volunteering in Sierra Leone treating Ebola patients told Metro newspaper that medical staff were swamped.
"The main challenge here, though, is that the health authorities just don't have the infrastructure to cope. They're overwhelmed," Benjamin Black said.
A top doctor in charge of a Sierra Leone treatment centre died of the virus earlier this week.
A spokesman for the French foreign ministry said they were offering technical support and expertise on the ground in west Africa. And Liberia announced it was shutting all schools and placing "non-essential" government workers on 30 days' leave.
The virus crossing borders for the first time by plane could lead to new flight restrictions aimed at containing outbreaks, the world aviation agency said.
"Until now (the virus) had not impacted commercial aviation, but now we're affected," ICAO secretary general Raymond Benjamin said.
"We will have to act quickly."
