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.

Four more people linked to a cluster of transmissions at a ski resort in France tested positive for the coronavirus, bringing the total number of cases in Britain to eight, the health department announced Monday.

The newly introduced measures — which apply only in England — are among the first in Europe to allow health authorities to keep individuals in quarantine if public health professionals believe they may be at risk of spreading the virus.

The new 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 emphasised 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 centre, 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. Those on the flight were taken to the Kents Hill Park conference centre, about 50 miles northwest of London, for 14 days of quarantine.

By Monday morning, eight people in England had tested positive for the mew coronavirus, according to a statement from Prof. Chris Whitty, the department of health’s chief medical officer for England, doubling the known cases in the country.

“The new cases are all known contacts of a previously confirmed UK case, and the virus was passed on in France,” Prof. Whitty said in a statement.

“Experts at Public Health England continue to work hard tracing patient contacts from the UK cases.”