A patient diagnosed with coronavirus in England has become the first to catch the illness within the UK.
Chief medical officer Professor Chris Whitty said it was not yet clear if the virus had been passed on from somebody who had recently travelled abroad.
It marked the 20th confirmed case in the UK - 18 of which were in England, one in Northern Ireland and one in Wales.
Last night, a doctor from Surrey was feared to have fallen ill and is awaiting formal confirmation.
The GP - poised to be announced as the UK's 21st confirmed case - is understood to have not recently been to virus-hit northern Italy, China, Tenerife or Iran.
Officials were scrambling to work out if the doctor has treated patients in the time between catching the virus and falling ill today, The Guardian reported.
The news comes after a British man became the first UK citizen to die from coronavirus.
The man, who was on board the Diamond Princess cruise ship, was the sixth person from the vessel, which has been quarantined off the Japan's coast amid the outbreak, to have died.
Confirming the latest case in England, Prof Whitty said: "One further patient in England has tested positive for covid-19.
"The virus was passed on in the UK. It is not yet clear whether they contracted it directly or indirectly from an individual who had recently returned from abroad.
"This is being investigated and contact tracing has begun.
"The patient has been transferred to a specialist NHS infection centre at Guy's and St Thomas."
The Department of Health and Social Care (DHSC) said the original source of the virus was "unclear", adding that there was no "immediately identifiable link" to overseas travel.
According to Public Health England (PHE), one of the latest coronavirus cases was a resident in Surrey.
Dr Alison Barnett, centre director for PHE South East, said: "Public Health England is contacting people who had close contact with a confirmed case of covid-19.
"One of the latest cases is a resident of Surrey and we're working closely with NHS colleagues in that area as well as Surrey County Council to manage the situation and help reduce the risk of further cases.
"Close contacts will be given health advice about symptoms and emergency contact details to use if they become unwell in the 14 days after contact with the confirmed case.
"This tried and tested method will ensure we are able to minimise any risk to them and the wider public."
The World Health Organisation has raised its global risk assessment of covid-19 to its highest level, after the epidemic spread to sub-Saharan Africa and caused financial markets to plunge.
China is still the hardest-hit country and has most of the 85,000 cases worldwide and related deaths.
Globally, more than 80,000 people have been infected. About 2,800 have died - the vast majority in China's Hubei province. China confirmed another 327 cases - the lowest daily increase for a month - along with 44 deaths.