A woman who flew into London from China a few days ago is being treated for coronavirus, bringing the total number of UK cases to nine.
Chief medical officer Chris Whitty said the woman was transferred to a specialist NHS centre at Guy's and St Thomas' in central London.
Prof Whitty said the patient had contracted the virus in China.
Sources say she developed symptoms after landing at Heathrow, called NHS 111 and then tested positive.
It comes after Prof Paul Cosford, from Public Health England, earlier told the BBC that more UK cases were "highly likely".
Meanwhile, all 83 people being held in quarantine at Arrowe Park Hospital in the Wirral have been told their final set of test results for the coronavirus have come back negative, confirming they are free of the virus.
It is expected they will leave the accommodation on Thursday morning, having spent two weeks there in quarantine.
Earlier, British man Steve Walsh, one of the nine UK cases of coronavirus, left hospital having fully recovered.
Walsh, 53, from Hove, who has been linked to other cases of the virus, now poses "no risk to the public", NHS England said.
In a statement on his release from hospital, Walsh, a scout leader, said: "I want to give a big thank you to the NHS who have been great throughout and my thoughts are with everyone around the world who continues to be affected by the virus."
Doctors among nine cases
Of the nine people so far diagnosed with coronavirus in the UK, two are GPs.
Officials know that the pair worked at a nursing home, Worthing Hospital A&E and two GP practices between them.
Public Health England confirmed on Wednesday it has traced and advised all close contacts of the two GPs, including about 12 patients.
A total of 1750 people in the UK have tested negative for the virus.
Earlier, Prof Cosford, from Public Health England, said people returning to the UK from travelling abroad could bring in further cases of coronavirus.
There were a number of "countries of concern", he said.
On Tuesday, the World Health Organization said the official name for the disease caused by the coronavirus is Covid-19.
The overall number of infections is more than 44,000 on mainland China, with cases in more than 20 countries.
What are the symptoms of coronavirus and what can help stop its spread?
The main signs of infection are fever (high temperature) and a cough as well as shortness of breath and breathing difficulties.
Frequent hand washing with soap or gel, avoiding close contact with people who are ill and not touching your eyes, nose and mouth with unwashed hands, can help cut the risk of infection.
Catching coughs and sneezes in a tissue, binning it and washing your hands can minimise the risk of spreading disease.