Health officials have contacted hundreds of people who attended a conference in London, after it emerged someone subsequently diagnosed with coronavirus had been there.
The person, who has not been identified, was at the UK Bus Summit at the QEII Conference Centre last week.
Dr Yimmy Chow from Public Health England said the delegates had been informed as a precaution.
So far, nine people in the UK have been diagnosed with the virus, Covid-19.
Around 250 people from the nationwide bus and transport industry were listed as attending the annual summit on 6 February, in Westminster.
Transport Times, the organiser of the conference, sent an email on Thursday afternoon to attendees informing them that a person confirmed to have coronavirus had been at the event.
The email included advice from PHE urging delegates that no action was needed if they felt well, but if they developed symptoms such as a fever or cough they should stay indoors, avoid contact with others and call NHS 111.
The letter told people to follow the advice until 20 February, “even if your symptoms are minor”.
Dr Chow, a PHE consultant in health protection, said: “One of our main priorities has been to identify any people who we think have been in close contact with confirmed cases of Covid-19 to provide public health advice, as they may be at slightly increased risk of catching the virus.
“While the degree of contact conference delegates may have had with the case is unlikely to have been significant, we have taken a precautionary approach and informed them of the situation.”
According to the latest figures, more than 1,300 people are now known to have died from the virus, the majority in China.
According to the Press Association news agency, the conference case is not linked to the latest person in the UK to test positive for the virus earlier this week, a Chinese woman.
The woman, who caught the virus in China before flying to the UK, went to hospital in an Uber but PHE said the driver is not at “high risk”. It was the first case to be identified in London.
As of 14:00 GMT Thursday, tests for the virus have been carried out on 2,521 people in the UK – with all but nine being negative.
In addition to the patient being treated at St Thomas’ Hospital in London, the UK’s coronavirus cases include two Chinese nationals who tested positive in York.
Another cluster of cases began with British businessman Steve Walsh, who contracted the virus in Singapore and passed it to 11 people at a ski resort in France. Five of these returned to the UK. Mr Walsh has now recovered.
Meanwhile, more than 80 people who stayed in accommodation at Arrowe Park Hospital in Wirral for two weeks have left after testing negative for the new strain of coronavirus.
They are one of two groups of British nationals evacuated from Wuhan, with the second quarantined near Milton Keynes.
On Thursday, the head of NHS England Sir Simon Stevens warned that many more people may be forced to self-isolate as part of efforts to stop the coronavirus spreading in Britain.
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.
Anyone experiencing symptoms, even if mild, after travelling from mainland China, Thailand, Japan, Republic of Korea, Hong Kong, Taiwan, Singapore, Malaysia or Macau, is advised to stay indoors and call the NHS 111 phone service.
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