The World Health Organisation has declared the coronavirus outbreak an international public health emergency.
The WHO's emergency committee "almost unanimously" concluded it was an international emergency, said chair Didier Houssin, as the announcement was made tonight as the death toll rises to 170.
Speaking at a press conference in Geneva, Switzerland, Director-General of the WHO, Tedros Adhanom, said: "Over the past few weeks, we have witnessed the emergence of a previously unknown pathogen, which has escalated into an unprecedented outbreak, and which has been met by an unprecedented response.
"As I have said repeatedly since my return from Beijing, the Chinese government is to be congratulated for the extraordinary measures it has taken to contain the outbreak, despite the severe social and economic impact those measures are having on the Chinese people.
"We would have seen many more cases outside China by now - and probably deaths - if it were not for the government's efforts, and the progress they have made to protect their own people and the people of the world."
In a letter following WHO's announcement, the chief medical officers of England, Wales, Scotland and Northern Ireland said: "In light of the increasing number of cases in China and using existing and widely tested models, the four UK chief medical officers consider it prudent for our governments to escalate planning and preparation in case of a more widespread outbreak.
"For that reason, we are advising an increase of the UK risk level from low to moderate. This does not mean we think the risk to individuals in the UK has changed at this stage, but that government should plan for all eventualities."
They added that it is "likely" there will be individual cases in the UK, but that they are "confident in the ability of the NHS and HSC in Northern Ireland to manage these in a way that protects the public and provides high quality care".
The announcement comes just hours before an evacuation flight to bring Brits back to the UK is due to leave Wuhan city, where the virus outbreak began.
The UK Foreign Office revealed Brits are tonight being evacuated and will be held in quarantine at an NHS facility in the Wirall, near Liverpool, for 14 days after they land tomorrow.
General Dr Tedros Adhanom Ghebreyesus of the WHO said: "The main reason for this declaration is not because of what is happening in China, but because of what is happening in other countries.
"Our greatest concern is the potential for the virus to spread to countries with weaker health systems, and which are ill-prepared to deal with it."
Last week, WHO said it was "too early" to declare an international public health emergency but on Thursday today said action was needed to help countries to prepare for the possibility of it spreading further.
The new virus has now infected more people in China than fell ill during the 2002-2003 severe acute respiratory syndrome (Sars) outbreak. The number of cases has jumped to 7,711, surpassing the 5,327 people diagnosed with Sars.
The death toll, which rose to 170 on Thursday morning, is lower than the 348 people who died in China from Sars.
In the UK, 161 people have tested negative for the virus as of Thursday.
The evacuation flight to bring Brits back will leave Wuhan City tonight and land Friday before passengers are then held in an NHS facility on the Wirral for a quarantine period of 14 days, Foreign Secretary Dominic Raab has said.
The flight is due to leave Wuhan city at 5am local time on Friday morning, which is 9pm on Thursday evening UK time.
The flight will land at RAF Brize Norton in Oxfordshire where UK nationals will disembark. Fifty foreigners - mainly from EU countries and thought to be Spanish - will also be on the evacuation flight which will head to Spain afterwards.
Janelle Holmes, chief executive of Wirral University Hospital, sent a message to staff on Thursday evening, saying: "Around 100 British citizens will be travelling to the UK from China tomorrow.
"We will be welcoming and housing them in the accommodation block at Arrowe Park Hospital.
"Before arrival they will be screened for symptoms. If anyone becomes unwell after arrival they will be treated following appropriate protocols."
British nationals have been asked to make their own way to the airport, and it is understood the British Consulate has provided letters to help people in cars get past security checkpoints.
Passengers say they have been told only to take hand luggage on the flight.
Jeff Siddle, from Northumberland, told the BBC his family faced a "terrible dilemma" after he and his nine-year-old daughter were told they could fly back - but not his Chinese wife, who has a permanent residency visa for the UK.
The WHO has said the "whole world needs to be on alert" over the new coronavirus outbreak.
The number of cases of coronavirus has jumped to 7,711, with 170 deaths.
India confirmed its first case on Thursday, as did the Philippines.
This comes as the first person-to-person spread of coronavirus in the United States has been confirmed in Illinois.
Meanwhile, the US Centers for Disease Control and Prevention has confirmed that a patient in Illinois has contracted the virus after their wife from Chicago became the second confirmed case of coronavirus in the US.
The man, who is in his 60s, caught the virus after his wife brought it back from Wuhan.
He is in a good condition despite some existing medical conditions while his wife is still in quarantine at a hospital.
Dr. Nancy Messonnier, director of the National Center for Immunization and Respiratory Diseases, told CNBC: "This is a very serious public health situation.
"Moving forward, we can expect to see more cases, and more cases means more potential for person-to-person spread."
