Health officials are urgently trying to trace those who came into contact with two people diagnosed with coronavirus in the UK.
Public Health England (PHE) confirmed that the two people taken ill – who are members of the same family – had been staying in York when they became unwell.
The pair were staying at the Staycity apartment-hotel in the city and were taken to hospital on Wednesday night.
The firm has said the apartment involved has been thoroughly disinfected and PHE has been providing support.
The two people diagnosed with the virus are being treated by Newcastle upon Tyne Hospitals NHS Foundation Trust in its specialist Airborne High Consequences Infectious Disease Centre (HCID).
It is understood that they travelled to the UK from China recently and are undergoing treatment at the Newcastle Royal Victoria Infirmary.
Professor Sharon Peacock, director of the National Infection Service at PHE, said: “Public Health England is contacting people who had close contact with the confirmed cases.
“The two cases were staying in York when they became unwell.
“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 cases.
“This tried-and-tested method will ensure we are able to minimise any risk to them and the wider public.”
Earlier, Prof Peacock said that while staff are working to trace people who have been in contact with the pair, they do not currently have “any idea” of how high that number might be.
The PHE definition of close contact is being within two metres of the infected person for 15 minutes.
It comes after more than 80 Britons on an evacuation flight from the Chinese city at the centre of the outbreak landed back in the UK.
The flight, carrying 83 Britons and 27 non-UK nationals, mostly from EU countries, arrived at the Brize Norton RAF base in Oxfordshire at around 1.30pm.
The UK passengers are being taken to Arrowe Park Hospital in Wirral for a quarantine period of 14 days, where they will be housed in an NHS staff accommodation block with access to the internet.
Driving on the M6, Liam Musgrove passed the convoy as it travelled on Friday evening.
“The experience was harrowing and quite surreal,” the 28-year-old from Manchester told the PA news agency.
“Seeing such an organised operation in place, it really puts into perspective what a deadly virus this could be.”
While in quarantine, the evacuated passengers are being given fully furnished rooms, food, laundry facilities and have access to a team of medical staff who will closely monitor their condition.
Kitchens are available for those who wish to self-cater, and families are being kept together, with games consoles, toys and cots provided.
Ministers said the Government will send another plane to coronavirus-hit Wuhan to rescue British citizens if needed.
Families had been told that relatives with Chinese passports would be unable to join them after Chinese officials denied them permission to leave the country.
That decision was reversed hours before the plane was due to depart, but some people did not have time to get to the airport.
PA understands that the Foreign Office (FCO) is working with EU countries to add British passengers to any rescue flights they may charter back from Wuhan.
The evacuation flight came after the UK’s four chief medical officers raised the risk level of the illness from low to moderate and the World Health Organisation (WHO) declared an international public health emergency.
Chinese health officials said on Friday morning that the death toll in the country from the virus had risen to 213, with the number of known cases rising from 7,711 to 9,962.
No deaths have occurred outside China, although cases have been confirmed across at least 23 countries.
The number of coronavirus cases worldwide has surpassed that of the Sars epidemic, although death rates are lower.
Many other countries, including Australia, South Korea, Singapore and New Zealand, have said they plan to quarantine evacuees for two weeks to avoid spread of the virus.