Six people who travelled to the UK from the epicentre of the coronavirus outbreak are being tested in UK hospitals after showing signs of the SARS-like infection.
Three patients are being treated in Edinburgh, with two in Glasgow and one in Belfast.
Prof Juergen Haas, head of infection medicine at Edinburgh University, said he believes there will be many more cases from other cities in the UK.
He said the Scottish patients had respiratory symptoms and had been in Wuhan, ground zero for the outbreak in China, in the last 14 days.
The Prime Minister is being kept updated on the situation, a Number 10 spokesman said.
The patients were suffering flu-like symptoms after arriving Britain, and it is understood they travelled here on a flight to London Heathrow Airport.
Infection outbreak and control measures are in place around a ward at Glasgow's Queen Elizabeth University Hospital.
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It comes after two police stations in Bristol were closed after a Chinese national who was detained started showing flu-like symptoms.
It was feared he had come into contact with people from the Wuhan area - but Public Health England later said this was not the case, Bristol Live reports.
The outbreak has killed at least 17 people and infected more than 630 others in China since it emerged late last month, and it has since spread to countries including the US, Singapore, Japan, South Korea and Thailand.
Initial tests in Scotland had failed to rule out coronavirus as authorities around the world worked to prevent a global pandemic.
None of the patients have been confirmed as having the disease.
They all travelled to Scotland from Wuhan, where the outbreak is thought to have originated, within the past two weeks and are showing symptoms of respiratory trouble, a red flag for the virus.
A source said infection outbreak and control measures have been put in place around a ward at the Glasgow hospital where one patient was being treated in isolation.
Staff must wear sterile suits.
The source said: “There was no doubt that the situation was being taken seriously because of the symptoms being displayed and the specific origin of travel.
“The patient came through London to Glasgow and after the symptoms were flagged up no chances were taken.
“The tests that were carried out could not immediately isolate what the condition might be and it may take a bit longer to be absolutely sure what doctors are dealing with.
“Obviously they are erring on the side of caution in the meantime.”
Flights between Wuhan - a a city of 11million people - and London were halted as the central Chinese city was put into lockdown in a desperate bid to prevent the virus from spreading.
Residents have been told not to leave the city.
Planes at Wuhan's airport have been grounded, and bus, train and ferry services have been cancelled.
Motorway toll booths have been shut and roads blocked, cutting off exits.
Guards were patrolling highways, one resident told Reuters.
There was panic in Wuhan as residents stormed shops that sell masks and supermarket shelves were cleared of food and other supplies.
Neighbouring Huanggang, a city of about seven million people, has implemented a similar lockdown, suspending transport and ordering places such as cinemas and internet cafes to close.
"The lockdown of 11 million people is unprecedented in public health history," Gauden Galea, the World Health Organisation's (WHO) representative in Beijing, said.
A Number 10 spokesman said: "The Prime Minister is being kept updated.
"Ministers and officials will keep the situation under close review."
The Prime Minster's deputy spokesman said of the measures being taken in Scotland: "These measures are purely precautionary."
The NHS is "ready to respond appropriately" to any cases of coronavirus that emerge in the UK, Health Secretary Matt Hancock has said.
In a statement to the Commons on Thursday, he said that while "there is an increased likelihood that cases may arise in this country, we are well prepared and well equipped to deal with them".
He said: "This is a rapidly developing situation and the number of deaths and the number of cases is likely to be higher than those that have been confirmed so far, and I expect them to rise further."
Mr Hancock said "most people" affected have experienced cold and flu symptoms, though some cases have proved fatal.
"We have been closely monitoring the situation in Wuhan and have put in place proportionate, precautionary measures," he said.
"Since yesterday, Public Health England officials have been carrying out enhanced monitoring of direct flights from Wuhan city and all passengers on direct flights from China will receive information on what to do if they fall ill."
He said England's chief medical officer, Professor Chris Whitty, is in contact with international experts and his counterparts to monitor the situation.
Mr Hancock said: "The chief medical officer has revised the risk to the UK population from very low to low, and has concluded that while there is an increased likelihood that cases may arise in this country, we are well prepared and well equipped to deal with them.
"The UK is one of the first countries to develop a world-leading test for coronavirus, the NHS is ready to respond appropriately to any cases that emerge, clinicians in both primary and secondary care have already received advice covering initial detection and investigation of possible cases, infection control and diagnostics.
"The public can be assured that the whole of the UK is always well prepared for these type of outbreaks and we will remain vigilant and keep our response under constant review in light of emerging scientific evidence."
It is feared the virus will spread rapidly in China and abroad as hundreds of millions of people travel for the week-long Lunar New Year holiday, which begins on Saturday.
The new strain of coronavirus is believed to have spread to humans at a market in Wuhan were live animals were illegally sold.
A group of experts said in a report that it appeared the virus was passed on to humans from snakes which had been infected by bats.
Government medical adviser Zhong Nanshan had also identified badgers and rats as possible sources.
The WHO will decide on Thursday whether to declare the outbreak a global health emergency, which would step up the international response.
The actual number of cases could be much higher than the figures released by China.
Imperial College London said it estimated a total of 4,000 cases in Wuhan alone as of January 18 based on the number of cases reported in China and elsewhere.
There is no vaccine for the virus, which can spread through respiratory transmission.
Symptoms include fever, difficulty in breathing and cough, similar to many other respiratory illnesses, and it can lead to pneumonia.
Meanwhile, the Foreign and Commonwealth Office has updated its travel advice for China, with a spokesman saying: "In light of the latest medical information, including reports of some person-to-person transmission, and the Chinese authorities' own advice, we are now advising against all but essential travel to Wuhan.
"The safety and security of British nationals is always our primary concern and we advise British nationals travelling to China to remain vigilant and check our travel advice on gov.uk."
