LONDON — Britain’s health department declared the new coronavirus an “imminent threat” to public health and announced a series of measures to combat the spread of the virus, a sign of the seriousness with which local health authorities are treating the fears of the epidemic.
The newly introduced measures — which apply only in England — are among the first in Europe to allow the health authorities to keep individuals in quarantine if public health professionals believe they may be at risk of spreading the virus.
Four more people in Britain linked to a cluster of transmissions at a ski resort in France tested positive for the coronavirus, bringing the total number of cases in the country to eight, the health department announced Monday.
The coronavirus has sickened more than 40,500 people, mostly in China, and at least 910 people have died since the virus first emerged in Wuhan, a city of 11 million people in the central part of the country late last year. Since that time, the virus has also spread to at least 24 countries, triggering fears of a global pandemic.
The Department of Health and Social Care emphasized that the risk of contracting the coronavirus in Britain remained “moderate,” even as the government empowered the health authorities to forcibly quarantine people. It also designated a hospital, near Liverpool, and a conference center, northwest of London, as isolation facilities for those placed under quarantine.
“I will do everything in my power to keep people in this country safe,” Matt Hancock, Britain’s health secretary, said in a statement. “We are taking every possible step to control the outbreak of coronavirus.”
He added that it meant health care providers would be “supported with additional legal powers to keep people safe across the country,” noting transmission of the coronavirus would “constitute a serious threat.”
The new measures were announced a day after a repatriation flight from Hubei Province — Wuhan is the largest city in the area — carrying about 200 citizens from Britain and elsewhere landed at an air force base in central England. British passengers were taken to the Kents Hill Park conference center, about 50 miles northwest of London, for 14 days of quarantine.
Twenty Germans who were on board the evacuation flight were brought to a Red Cross hospital in Berlin. Like 126 Germans who were picked up from Wuhan earlier this month, those who arrived at the weekend agreed to a quarantine time of two weeks. There are 14 known cases of the virus across Germany.
By Monday morning, eight people in England had tested positive for the coronavirus, according to a statement from Professor Chris Whitty, the Department of Health’s Chief Medical Officer for England, doubling from a day earlier the known cases in the country.
“The new cases are all known contacts of a previously confirmed U.K. case, and the virus was passed on in France,” Professor Whitty said in a statement. “Experts at Public Health England continue to work hard tracing patient contacts from the U.K. cases. They successfully identified these individuals and ensured the appropriate support was provided.”
The new cases in Britain are linked to cases in France, according to the French health authorities which all trace back to a group of British citizens staying in a chalet in the Alpine village of Les Contamines-Montjoie, near Switzerland, late last month.
A British man at the center of the transmissions is believed to have contracted the coronavirus while attending a conference in Singapore, before flying to Geneva on Jan. 24, and from there the village, where he shared lodgings with a group of fellow Britons.
The man then returned to Britain on Jan. 28 on an easyJet flight, the budget airline confirmed in an emailed statement. He is among the eight people in Britain who have tested positive for the virus.
EasyJet said in an emailed statement that it had been notified by the public health authorities that a customer who had recently traveled on flight EZS8481 from Geneva to London Gatwick on Jan. 28 had since received a coronavirus diagnosis.
“Public Health England is contacting all passengers who were seated in the vicinity of the customer,” the company said in a statement, but noted that since the man had not been experiencing any symptoms, the risk to others on board the flight was “very low.”
At least one of the people who tested positive for the virus was confirmed to be from Brighton, a seaside town on England’s south coast, and the BBC reported on Monday that the County Oak medical center there had to shut its doors after a member of staff tested positive for the virus.
A message on the center’s answering machine indicated it had been closed for an “urgent operational health and safety reason.”
Public Health England confirmed that two of the cases of coronavirus in Britain were health care workers. Yvonne Doyle, Public Health England’s medical director, said in a statement that all of the new cases announced on Monday were “closely linked to one another.”
“Our priority has been to speak to those who have close and sustained contact with confirmed cases, so we can advise them on what they can do to limit the spread of the virus,” she said. “We are now working urgently to identify all patients and other health care workers who may have come into close contact, and at this stage we believe this to be a relatively small number.”
A pub near Brighton in Hove, The Grenadier, said in a statement on its Facebook page that a person confirmed to have the virus had visited the establishment, but that Public Health England had determined there was minimal risk, and it was following official advice to remain open.
At least five other Britons who stayed in the chalet and are still in France have tested positive for the coronavirus, said Agnès Buzyn, France’s health minister. They are among at least 11 people in France who have tested positive for the disease.
A 9-year-old boy was among the British people who contracted the virus in the ski village. According to a spokeswoman for the region, the child is a permanent resident of the village, where he lives with his father, who also contracted the virus, and two siblings. His mother is currently in Britain.
He attended a local school in Les Contamines-Montjoie and took French lessons in two nearby schools in Saint-Gervais and Thonon-Les-Bains. As a precaution, the three schools have all been closed for the week and fellow students are being tested.
Six other British people staying in the chalet have all tested negative for the virus, according to the head of France’s national health agency, Jérome Salomon.
The French health authorities said they were still in the process of determining exactly how many people were staying in the chalet and who may have come into contact with those carrying the coronavirus.
Ms. Buzyn, the health minister, visited the ski resort on Sunday.
“It is important to reassure the people of this village,” she said. “We have to tell them that there is no risk when you meet people on the street, it’s not the same as being in contact with an infected person.”
“It’s about close, sustained, face-to-face or physical contact,” she added.
A crisis unit has been opened in Les Contamines-Montjoie, where testing is underway to determine if there are further cases of the coronavirus.
On Sunday night, Mr. Salomon, the head of the national health agency, announced that results from 21 samples had all tested negative and that 25 others were still being analyzed.
“It’s already very good news,” he said.
Etienne Jacquet, the mayor of Les Contamines-Montjoie, said in a phone interview that students who might have been in contact with the infected child underwent tests as a priority on Sunday. He said the precautionary measures made the village, in his opinion, the “most secure city in France” when it came to the coronavirus.
“In Les Contamines-Montjoie life goes on normally,” Mr. Jacquet said. “For the moment there is absolutely no crisis.”
Megan Specia reported from London and Constant Méheut reported from Paris. Christopher F. Schuetze contributed reporting from Berlin.