Eight people have now tested positive for coronavirus in England, the Department of Health has announced.
The virus originated in China, and over 1,100 people have already died - globally there are nearly 45000 confirmed cases.
More than 70 people had been tested for suspected coronavirus in the UK, but none had been confirmed as having contracted it until now.
Here's everything you need to know:
Where are the UK cases?
Paul Hunter, Professor in Medicine at the University of East Anglia, said the UK cases were "not surprising and almost inevitable".
It is understood the patients are not in the Wirral area, where a special facility has been set up to quarantine those returning from Wuhan.
One of the three people diagnosed with coronavirus in Britain is a student at the University of York.
Two of the patients are being treated in an NHS specialist disease centre in Newcastle and are members of the same family, Public Health England (PHE) said.
The third person in the UK to be diagnosed with coronavirus did not catch it in mainland China, the chief medical officer has said.
The patient, who caught the infection elsewhere in Asia, was diagnosed in Brighton, it is understood.
The Chief Medical Officer Professor Chris Whitty said the fourth patient was a known contact of a previous UK case, and that the virus was passed on in France.
It comes shortly after a British man in Majorca was confirmed to have tested positive for the virus, and as more than 200 people return to the UK on the Government's last repatriation flight on Sunday morning.
The Majorca case is said to be one of four members of a British family who were taken into observation on Friday. They came into contact with someone in France who was later diagnosed with the virus, but his wife and two daughters have tested negative and show no symptoms.
Five Britons have tested positive for coronavirus in France while on holiday in the Alps, the country's health minister has confirmed.
Four adults and a child have also been diagnosed with the virus, after staying in the same French Alps ski chalet and coming into contact with a Briton who had recently returned from Singapore.
What measures are in place to stop the virus spreading?
Chief medical officer Professor Chris Whitty said: "The patients are receiving specialist NHS care, and we are using tried and tested infection control procedures to prevent further spread of the virus.
"The NHS is extremely well-prepared and used to managing infections and we are already working rapidly to identify any contacts the patients had, to prevent further spread.
"We have been preparing for UK cases of novel coronavirus and we have robust infection control measures in place to respond immediately.
Flights, trains and public transport including buses, subway and ferry services have been temporarily closed in China to help stop the outbreak (Photo: Getty Images)
"We are continuing to work closely with the World Health Organisation and the international community as the outbreak in China develops to ensure we are ready for all eventualities."
He said: "The NHS is well able to nurse people with this novel coronavirus as it has successfully and safely managed a number of cases of both SARS and MERS in the past. With the information available it is not possible to judge what risk if any there may be of spread within the community.”
The news of the UK's first confirmed cases emerged as more than 80 Britons on an evacuation flight from the Chinese city at the centre of the outbreak were due to land in the UK.
The flight is expected to arrive at Brize Norton RAF base in Oxfordshire around 1pm on 31 January.
Cabinet Office Minister Michael Gove said the UK Government will send another plane to Wuhan to rescue British citizens if necessary.
He told Sky News: "The flight which is the air at the moment is not the end of our efforts. It is only one part that we are doing in order to keep people safe.
"We will do everything we can to ensure that every UK citizen, every UK national, every member of their family is contacted, supported.
"If we need to, we will send another plane. We will be working with other countries to ensure the safety and security of every UK citizen and national."
Every hospital in England is being asked to create “priority assessment pods” for patients with suspected coronavirus, the NHS has said.
The new measure means that A&E departments will be able to direct people who think they have symptoms of the coronavirus to a secure area away from other patients, where they can call specialist NHS 111 teams on a dedicated phone. The secure areas are expected this month.
Patients concerned they may have the virus are still advised to isolate themselves and call 111. But the measure is intended to prevent patients who do arrive at hospital from mixing with vulnerable patients.
Should I be worried?
The coronavirus has been compared to the 2002-03 outbreak of SARS which infected 8,000 people in 37 countries and killed nearly 800 people.
The UN criticised China for concealing the scale of the SARS virus, but this time around the Chinese Government has responded to the new strain of the coronavirus with tough measures.
Chinese scientists have shared this new pathogen’s genome with researchers around the world, helping medics to identify fresh cases.
Several cities have been quarantined, notably China’s seventh largest, Wuhan, a transport hub with direct flights to major airports in Asia, the US and Europe, including Heathrow.
What is the coronavirus?
The virus is a new strain of coronavirus, which is in the same family as SARS and MERS (Middle East respiratory syndrome).
This particular strain originated in Wuhan City, Hubei Province, the largest city in central China.
Coronaviruses are a large family of viruses, with the Centers for Disease Control and Prevention (CDC) explaining they usually cause “mild to moderate upper-respiratory tract illnesses”, like the common cold.
Most people get infected with these viruses at some point during their lives, although they usually only last for a short period of time.
Symptoms of the virus may include:
runny noseheadachecoughsore throatfevera general feeling of being unwell
There are currently no vaccines to protect against coronavirus infection, but there are ways to help reduce your risk of contracting it.
The CDC advise:
washing your hands often with soap and water for at least 20 secondsavoid touching your eyes, nose, or mouth with unwashed handsavoid close contact with people who are sick
If you are experiencing cold-like symptoms, you can help reduce the risk of spreading it by staying at home while you are ill, and avoiding close contact with others.