But there are no known cases in the UK, Mr Hancock said, which was "well prepared" to deal with an outbreak.
Nathalie MacDermott of King's College London said on Science Alert that the virus is most likely spreading through droplets in the air passed on by people sneezing or coughing.
Chinese authorities Thursday moved to lock down three cities that are home to more than 18 million people in an unprecedented effort to contain a new virus that has sickened hundreds and spread to other parts of the world during the busy Lunar New Year travel period.
The man is now quarantined in a hospital outside of Seattle.
Prime Minister Boris Johnson's spokesman said the tests were "purely precautionary".
The researchers note that there is a lack of treatments and effective vaccines against coronaviruses - some vaccines have been developed but so far only tested on animals.
Hours later, authorities in neighbouring Huanggang announced public transport and train services would be suspended at midnight, while people were told to not leave the city of 7.5 million.
The UK is monitoring flights arriving from China as a precaution.
The risk to anyone in the United Kingdom who has not recently travelled to China remains low and we should not be unduly anxious but one thing is certain - this story is only going to grow in the coming days as the virus spreads further and to greater numbers of people. Two of those being tested had been diagnosed with flu after travelling to Wuhan in China - the origin of the global outbreak.
On Tuesday, the Chinese Communist Party asked provincial leaders to be as transparent as possible and warned against concealing the outbreak of infections or putting political interests ahead of public health.
Authorities around the world have announced screening measures for passengers from China.
Meanwhile, the official death toll in China has risen to 26 with more than 830 confirmed cases.
More than 500 people are believed to have been infected, prompting the World Health Organisation to hold an emergency meeting.
The U.N. health agency defines a global emergency as an "extraordinary event" that constitutes a risk to other countries and requires a coordinated worldwide response. Most of the 17 victims were elderly and suffered from other chronic diseases including Parkinson's disease and diabetes.
"In my view it's very unlikely to be a snake because the jump from a reptile to a person is evolutionarily quite a long way", said Jones, who added that while snake handling is common in the region, he is not aware of any individuals contracting this kind of virus after direct handling of snakes.
Now known as 2019-nCoV, the virus is understood to be a new strain of coronavirus not previously identified in humans.
The virus has caused alarm in China and overseas because of its genetic similarities to Severe Acute Respiratory Syndrome (Sars), which killed almost 650 people across mainland China and Hong Kong in 2002-2003. Current thinking is that the animal hosts may have been snakes, although a seafood market in Wuhan that was illegally trading in live animals is also being investigated. The market has been shut down since the beginning of the year.