Schools in the UK could be closed for more than two months if the coronavirus outbreak intensifies and becomes "out of control", England's chief medical officer has said.
Professor Chris Whitty's warning comes as two tested positive for COVID-19 in Derbyshire and Northern Ireland recorded its first case - bringing the total confirmed cases in the UK to 16.
He also said onward transmission between people in the UK without recent travel to affected virus hotspots was "just a matter of time".
Professor Whitty said if the virus becomes a global epidemic there could be a potential "social cost", which may include cutting the number of mass gatherings and shutting schools for several weeks.
He said: "One of the things that's really clear with this virus, much more so than flu, is that anything we do we're going to have to do for quite a long period of time, probably more than two months.
"The implications of that are non-trivial, so we need to think that through carefully.
"This is something we face as really quite a serious problem for society potentially if this goes out of control."
Professor Whitty added: "If this becomes a global epidemic then the UK will get it, and if it does not become a global epidemic, the UK is perfectly capable of containing and getting rid of individual cases leading to onward transmission."
One of the new cases - a parent of a pupil at Burbage Primary in Buxton, Derbyshire - contracted the virus in Tenerife, where 168 Britons have been kept quarantined in a hotel this week. The school has now been shut.
A GP surgery, Buxton Medical Practice, has also been closed as a result of the other confirmed case. The person contracted the virus in Italy, which has become the worst affected country in Europe with more than 400 cases and 14 deaths.
Several schools have closed over fears of COVID-19 contact.
Others have sent pupils home, including Prince George and Princess Charlotte's primary school Thomas's Battersea.
But Public Health England's general advice is for them not to shut.
The government has said people returning from the coronavirus epicentre - Hubei province in China, as well as Iran, lockdown areas in northern Italy, and special care zones in South Korea - should self-isolate at home and call NHS 111.
People returning from a number of other countries including the rest of China and Korea, Japan, Hong Kong and Singapore should self-isolate if they develop symptoms of cough or fever or shortness of breath.
It also said that those returning from Vietnam, Cambodia, Laos, Myanmar and northern Italy above Pisa should self-isolate if they show symptoms.
So far there have been at least 2,810 deaths worldwide, the vast majority in China, and at least 82,550 confirmed infections, most affecting Chinese citizens.