British Airways has cancelled all flights to and from Italy after the entire nation was placed in lockdown in response to the coronavirus outbreak.
All public gatherings have been banned, sports events including football matches are suspended, and movement is being severely restricted across Italy in a bid to contain COVID-19 , the disease caused by coronavirus.
People were frantically buying up food and other essentials at supermarkets shortly after the announcement, Italian media reported.
Italy is Europe's worst-hit nation in the outbreak with 463 virus-related deaths , an increase of almost 100 in a 24-hour period, and more than 9,000 confirmed infections in just over two weeks.
Until 3 April, around 60 million people will effectively be under quarantine by the strict measures which had already been introduced in northern and some central areas over the weekend.
It comes as an Italian doctor wrote in a lengthy Facebook post that his hospital was being "overwhelmed" by the "tsunami" of patients.
Dr Daniele Macchini, who works at Humanitas Gavazzeni hospital in Bergamo, northern Italy, said: "The war has literally exploded and the battles are uninterrupted day and night.
"The display boards with the names of the sick, of different colours depending on the operating unit they belong to, are now all red and instead of the surgical operation there is the diagnosis, which is always the same cursed: bilateral interstitial pneumonia.
"The results of the swabs now come one after the other: positive, positive, positive. Suddenly the emergency room is collapsing."
People arriving in the UK from anywhere in Italy have been told by the Foreign Office to self-isolate for 14 days.
And Britons have also been warned against all but essential travel to the whole of the country.
Italy's Prime Minister Giuseppe Conte is urging the public to stay at home, saying: "The future depends on us and everyone must do their part."
He said people should not move around apart from for work and emergencies, and the closure of schools and universities across the country is being extended to 3 April.
He also said public transport will remain operational.
Leading politicians have accused Mr Conte of not going far enough, with former deputy PM Matteo Salvini calling on the government to "close everything immediately, without leaving room for doubts or interpretations".
Lombardy president Attilio Fontana called for "even more stringent rules" so "we can overcome this emergency".
A statement from the Foreign Office said: "We have amended our travel advice to recommend against all but essential travel to Italy. The safety of British nationals is always our number one priority.
"The advice is that anyone who arrives from Italy subsequent to Italian government decision should now self-isolate for 14 days."
More than 300 of Italy's fatalities are in the Lombardy region - which includes the country's financial capital, Milan.
About 5% of confirmed cases in Italy have been fatal so far, making the fatality rate higher than in other parts of the world, where scientists have tentatively estimated it to be between 1-3%. The fatality rate in Lombardy stands at 6%.
It is not clear to what extent Italy has been testing people with minor symptoms or how long the virus had been circulating in the country before it was detected, which could contribute to the apparently higher fatality rate.
Lombardy is one of five regions which already had areas in lockdown in a so-called "red zone", with cinemas, theatres and museums closed and restaurant hours restricted.
The measures had affected 10 million residents in the whole of Lombardy and another six million in the provinces of Modena, Parma, Piacenza, Reggio Emilia, Rimini, Pesaro and Urbino, Alessandria, Asti, Novara, Verbano-Cusio-Ossola, Vercelli, Padua, Treviso and the tourist hotspot of Venice.
Mr Conte will sign a new decree and the nationwide limitations will be introduced in the morning.
He told reporters that restrictions introduced two days ago were no longer sufficient and they would have to be extended to the whole country.
The PM said: "There won't be just a red zone," adding: "There will be Italy" as a protected area.
Mr Conte also criticised young people in much of Italy who have been gathering at night to socialise during the public health emergency that started on 21 February.
"This nightlife... we can't allow this any more," he said.
Meanwhile, six inmates have died and several others have climbed on to the roof of a jail following protests across various prisons in Italy over limits on direct contact between inmates and their families.
In the south, Puglia, Basilicata, Calabria, Campania and Molise have seen just dozens of COVID-19 cases between them and a handful of deaths.
In a bid to deter a mass influx, southern regions issued decrees on Sunday telling people who do arrive from northern red zones that they had to go into quarantine for two weeks.
:: Listen to the Daily podcast on Apple Podcasts , Google Podcasts , Spotify , Spreaker
Earlier on Monday, Italy shut all of its ski resorts and Mr Conte said he would use "massive shock therapy" to battle the outbreak.
More than 3,900 people have died across the world, the vast majority in mainland China, the epicentre of the outbreak.
"Now that the virus has a foothold in so many countries, the threat of a pandemic has become very real," said World Health Organisation Director-General Tedros Adhanom Ghebreyesus.
But he welcomed Italy's tough measures, noting four countries - China, South Korea, Italy and Iran - accounted for 93% of cases worldwide.
In other coronavirus developments:
Virus Outbreak: Global Emergency - Watch a special Sky News programme on coronavirus at 6pm weekdays
Virus Outbreak: Your questions answered #AskSkyNews at 12.30pm weekdays
Are you a British citizen stuck in northern Italy? Get in touch with your story:
:: WhatsApp - 07583 000853
:: Email - email@example.com
:: 'Your Report' on Sky News apps