The third person to be diagnosed with coronavirus in the UK is a British National who became ill after travelling to Singapore, ITV News understands.
The patient, who has been confirmed as male and is thought to be middle-aged, has been taken to Guy's and St Thomas' Hospital in London for treatment following his diagnosis in Brighton.
Health officials are not understood to be "contact tracing" people on any Asia-UK flight the latest sufferer may have travelled on.
Meanwhile a Chinese doctor who got into trouble with authorities for issuing an early warning about the outbreak has died after contracting the illness, a hospital reported.
It comes as the Government expanded its list of countries and territories which it advised travellers to self-isolate and call NHS 111 after visiting if they begin feeling unwell.
As well as mainland China, the list now includes Hong Kong, Taiwan, Japan, Malaysia, South Korea and Macau.
Anyone arriving from these locations should stay indoors and avoid contact with other people if they develop symptoms such as a cough, fever or shortness of breath, the advice warns.
Explaining the updated advice, England's Chief Medical Officer Professor Chris Whitty said: "These countries have been identified because of the volume of air travel from affected areas, understanding of other travel routes and number of reported cases.
"This list will be kept under review."
Anyone with symptoms will be tested for coronavirus.
Prof Whitty added: "We knew this ratchet up might well happen and this is the moment where we feel it's prudent... to make this shift.
"What we have got is a situation where very high risk remains in Wuhan and Hubei, a high risk in the rest of China, but much lower than in Wuhan and Hubei, and then a much smaller risk in a number of countries, and unsurprisingly countries where the greatest risk is in terms of new cases are the ones which have the greatest international traffic with China, and that is exactly as you would expect."
He said there is no evidence of sustained person-to-person onward transmission of the virus outside China.
Currently more than 28,000 people, the majority in China, have contracted the coronavirus and at least 565 have died.
The Department of Health said it is "confident" these numbers are estimates and that as many as 100,000 people may have been infected.
Last week, Public Health England confirmed one of the two people who previously tested positive for coronavirus is a student at the University of York and the other person is a relative of theirs.
The pair are being treated at a specialist facility in Newcastle.
Earlier on Thursday, China's ambassador to the UK urged the British government to avoid causing "panic" - a day after the UK urged British nationals in China to return home.
Liu Xiaoming said a "cool-headed" and "objective" approach was needed to stop the disease, as he criticised the response of some foreign countries about their handling of the situation.
He said there had been open communication between the UK and China over the virus and they were working together to find a cure for the disease.
Health Secretary Matt Hancock told ITV News on Wednesday the UK has not ruled out the possibility of stopping flights arriving from China into the country in a bid to stop the spread of the disease.
Speaking about the response of the UK government, Mr Liu said: "We said there should be no panic, no overreaction.
"We advised the British side to take the professional advice of the World Health Organisation (WHO).
"The British side agreed but it seemed to me the words did not match the deeds."
He added the director general of the WHO, Tedros Adhanom Ghebreyesus, had commended China's response to stopping the spread of the disease and was also critical of overreactions by other nations.
Mr Liu said the disease had a relatively low mortality rate compared to other major outbreaks. He said currently, the mortality rate was 2.3%, while ebola was around 40% and SARS was nearly 20%.
He added: "I say again to the British government and the public, take a cool-headed view of what's going on in China.
"We don't think there should be such a panic... We believe epidemic is controllable, preventable and curable."
Mr Liu said China was taking the "strongest measures" against the disease, citing it had built two new hospitals to treat critically ill patients.
There has also been increased reports of hate crimes against Chinese people in the UK, something which Mr Liu said was due to "deep-seated racism".
He added: "I think the general public is very supportive.
"There are some cases of hatred, discrimination, against Chinese nationals...I think there are many reasons for it. Lack of understanding of the epidemic."
Mr Hancock said on Thursday the UK government was working to tackle "the very significant problem that they've got in China".
He added: "In terms of the plans that we've got, we have a full set of plans in place, including within the NHS, but also Public Health England, whose work so far to ensure that the contacts of those who have tested positive are chased - that work has been rapid and gone according to plan."
A letter from Professor Keith Willett, NHS strategic incident director for coronavirus, said the plans were necessary to avoid a "surge in emergency departments."
Patients who think they may have coronavirus symptoms would be directed away from A&E and towards one of the pods, where they could contact specialists on a dedicated phone line.
"Anyone with a cough, fever, or shortness of breath who attends hospital and has recently returned from China, will be advised to follow signs to NHS 111 pods and call for advice," a NHS spokesperson said.
The NHS hopes to have the pods up and running by Friday.
Doctors in China have also warned the disease may be passed on from pregnant women to their unborn children.
Meanwhile, 78 people with British passports - including crew - are in quarantine on the Diamond Princess cruise ship in Japan.
Health workers in Yokohama said 10 more people on the Princess Cruises vessel had tested positive for the disease, in addition to 10 on Wednesday when the ship was ordered to be isolated.
None of those who have tested positive are thought to be British.
There are no plans to fly anyone off the ship and back to the UK at the moment.
A separate ship in Hong Kong, the World Dream, has about 66 British passport-holders on board. Nobody on that ship has tested positive.
It is understood passengers are unable to leave the ship but are not in quarantine and can move around freely on board.