Countries around the world are already taking contingency steps against the spread of the Ebola virus, with politicians calling it a “very serious threat”.

The outbreak of the virus, which is the worst in history, has already claimed the lives of 670 in west Africa, with a US doctor in a critical condition after contracting the disease.

• Explainer: All you need to know about Ebola
• Top Ebola doctor dies of virus

Hong Kong says it is quarantining all people from Guinea, Sierra Leone and Liberia who were showing Ebola-like symptoms on arrival in the city, as fears grow worldwide about the spread of the deadly virus.

British Prime Minister David Cameron is said to also regard the virus as a “very serious threat”, and is meeting with crisis officials to assess preparations for a possible outbreak, according to a Fairfax report.

One man travelling from West Africa to Britain has been tested for Ebola, but the tests proved negative.

The director of global health at Public Health England, Dr Brian McCloskey, said that he thought it was clear the outbreak “is not under control”.

Hong Kong, a densely populated city of some seven million people, is particularly alert to the spread of viruses after Severe Acute Respiratory Syndrome (SARS) killed almost 300 people eleven years ago.

Local media reports in the southern Chinese city on Wednesday said that a woman who had visited Kenya had briefly been quarantined on her return to Hong Kong.

The South China Morning Post, citing an unnamed hospital source, said the woman had travelled to Kenya for a 17-day holiday and was briefly quarantined when she arrived back.

A health official confirmed to AFP that a woman showing symptoms, including fever and vomiting, had tested negative for Ebola after returning from Africa.

Meanwhile, fears that the Ebola outbreak could spread to Europe grew on Wednesday, with the EU allocating extra spending, while leading medical charity Doctors Without Borders warned the epidemic was out of control.

– with AAP