Video report by ITV News Correspondent Richard Pallot
The Chinese president has described the accelerating spread of coronavirus as a "grave situation", after holding a government meeting on the Lunar New Year holiday.
Xi Jinping's warning comes as more people have been inflected, more deaths reported and more cases confirmed around the world.
An unprecedented national lockdown has been rolled out to more than 50 million residents across several cities, as authorities try to limit the spread of the coronavirus, which has killed more than 40 people.
All 41 deaths have been in China, including 39 in Hubei province, the epicentre of the outbreak, and one each in Hebei and Heilongjiang provinces.
In a meeting with state officials, President Xi demanded all patients to be put in a centralized quarantine for treatment - though that may prove difficult with 1,300 cases already confirmed.
Five are in neighbouring Hong Kong - which has declared its highest level of emergency.
As well a closing Hong Kong schools for a fortnight and threatening prison for anyone not declaring their arrival from the mainland, Chief Executive Carrie Lam warned: "All cultural and sport visits within China are banned."
In the UK, authorities are trying to track down 2,000 people who have travelled from Wuhan - where the virus is thought to have originated.
France is the first country in Europe to announce three people have fallen ill with coronavirus.
The United States, Malaysia, South Korea, Hong Kong, Singapore and Macao have all had confirmed cases of the disease.
The Chinese military dispatched 450 medical staff, some with experience in past outbreaks including Sars and Ebola, who arrived in Wuhan late on Friday night to help treat the many patients hospitalised with viral pneumonia, the official Xinhua News Agency reported.
The new virus comes from a large family of what are known as coronaviruses, some causing nothing worse than a cold.
Symptoms include cough and fever and in more severe cases shortness of breath and pneumonia, which can be fatal.
Sars, which started in China in late 2002 and killed more than 750 people, was a coronavirus.
It is not clear how lethal the new coronavirus is, or even whether it is as dangerous as the ordinary flu, which kills tens of thousands of people every year in the US alone.
The rapid increase in reported deaths and illnesses does not necessarily mean the crisis is getting worse.
It could instead reflect better monitoring and reporting of the newly discovered virus, which can cause cold and flu-like symptoms, including cough, fever and shortness of breath, but can worsen to pneumonia.
The National Health Commission said Saturday it is bringing in medical teams from outside Hubei to help handle the outbreak, a day after videos circulating online showed frantic people in masks lined up for examinations and complaints that family members had been turned away at hospitals that were at capacity.
The Ministry of Commerce is coordinating an effort to supply more than two million masks and other products from elsewhere in the country, Xinhua said.
Wuhan is building a 1,000-bed prefab hospital to deal with the crisis, to be completed February 3, with plans to build a second as well.
With Chinese authorities afraid that public gatherings will hasten the spread of the virus, the outbreak put a damper on Lunar New Year.
Temples locked their doors, Beijing’s Forbidden City, Shanghai Disneyland and other major tourist destinations closed, and people cancelled restaurant reservations ahead of the holiday, normally a time of family reunions, sightseeing trips, fireworks displays and other festivities in the country of 1.4 billion people.
The vast majority of cases have been in and around Wuhan or involved people who visited the city or had personal connections to those infected.
About two dozen cases in all have been confirmed outside mainland China, nearly all of them in Asia: Hong Kong, Macao, South Korea, Japan, Singapore, Thailand, Taiwan, Vietnam, Nepal, Australia and Malaysia.
While most of the deaths have been older patients, a 36-year-old man in Hubei died on Thursday.