The World Health Organisation (WHO) has said it is "too early" to declare an international public health emergency over the coronavirus outbreak as six people are tested for the illness in the UK.

The Scottish Government has confirmed five people are being examined after presenting with symptoms of the illness.

Another patient is being tested to rule out coronavirus at Belfast's Royal Victoria Hospital, it is understood.

It came after infections expert Professor Jurgen Haas claimed there would likely be "many more cases" around the country.

On Thursday evening, the World Health Organisation said: "The Emergency Committee on the new #coronavirus (2019-nCoV) considered that it is still too early to declare a public health emergency of international concern given its restrictive and binary nature."

Speaking at a press conference, Dr Tedros Adhanom Ghebreyesus, director-general of the WHO, said: "Make no mistake, this is though an emergency in China.

"But it has not yet become a global health emergency.

"It may yet become one."

All but one of the 18 deaths have been in Hubei.

There are now more than 600 reported cases in countries including Japan, South Korea, Singapore, Thailand, the US and Vietnam.

Dr Tedros said the fact he was not declaring a public health emergency of international concern (PHEIC) "should not be taken as a sign that WHO does not think the situation is serious".

He added: "We are aware of media reports of suspected cases in other countries, but those cases are still being investigated."

While none of the UK cases has been confirmed as the virus so far, two of those being tested in Scotland had been diagnosed with influenza after travelling to Wuhan, China.

A further three people were "undergoing testing on a similar precautionary basis".

A spokesman for the Scottish Government said: "As the situation develops we will update should there be any confirmed cases of coronavirus, rather than provide a running update on cases being considered on a precautionary basis.

"We are co-orientating with Health Protection Scotland a daily Incident Management Team to continue to monitor the situation as it develops, including on the number of any potential cases going forward."

Downing Street said four suspected cases in Scotland were believed to involve Chinese nationals.

They all travelled to Scotland from Wuhan - where the outbreak is thought to have originated - within the past two weeks and were showing symptoms of respiratory trouble, a red flag for the virus.

Dr Tedros said: "We know that most of those who have died had underlying health conditions such as hypertension, diabetes or cardiovascular disease that weakened their immune systems.

"We know that there is human-to-human transmission in China, but for now it appears limited to family groups and health workers caring for infected patients.

"At this time, there is no evidence of human-to-human transmission outside China, but that doesn't mean it won't happen.

"There is still a lot we don't know. We don't know the source of this virus, we don't understand how easily it spreads and we don't fully understand its clinical features or severity."

Peter Piot, professor of global health and director of the London School of Hygiene & Tropical Medicine, said there were still "many missing pieces in the jigsaw puzzle".

He said: "We are at a critical phase in this outbreak. Regardless of the decision not to declare this a public health emergency of international concern, intensified international collaboration and more resources will be crucial to stopping this outbreak in its tracks.

"National authorities and the World Health Organisation will need to continue to monitor developments very closely.

"There are still many missing pieces in the jigsaw puzzle to fully understanding this new virus which is spreading rapidly across China, and most probably around the world.

"Over the coming days and weeks we will know much more, but there cannot be any complacency as to the need for global action.

"The good news is that the data to date suggest that this virus may have a lower mortality than Sars, we have a diagnostic test and there is greater transparency than decades gone by. And that is essential because you cannot deal with a potential pandemic in one country alone."

Prof Haas, head of infection medicine at the University of Edinburgh, said he believes there will probably be similar cases in "many other cities" in the UK.

He said: "We have currently three cases of suspected Wuhan coronavirus in Edinburgh and as far as I understand one case in Glasgow."

He said the cases emerged overnight, adding: "The situation will be pretty similar in pretty much all UK cities with a large number of Chinese students.

"It's not too surprising. My suspicion is that there will probably be many more cases in many other cities in the UK.

"None of the cases I know of have been confirmed."

He said there was only one laboratory testing for the virus, operated by Public Health England (PHE).

The professor said the cases had been flagged up through the PHE infection guidelines as they travelled to Wuhan within the last 14 days and were showing signs of respiratory symptoms.

The Chinese government has effectively locked down Wuhan, cancelling planes and trains there and in the nearby city of Huanggang.