Italy’s prime minister has said at least 16 million people are now under lock-down in Lombardy region and also in 14 provinces until early April.
The dramatic escalation in the country’s efforts to contain the new coronavirus will close gyms, pools, museums and ski resorts.
Weddings and funerals are also suspended under the new measures.
Italy is Europe’s worst-hit country and reported a steep rise in virus infections on Saturday.
The new measures, which also apply to financial centre Milan and tourist hotspot Venice will last until 3 April.
The death toll in Italy has passed 230, with officials reporting more than 50 deaths in 24 hours. The number of confirmed cases jumped by more than 1,200 to 5,883 on Saturday.
“We want to guarantee the health of our citizens. We understand that these measures will impose sacrifices, sometimes small and sometimes very big,” Prime Minister Giuseppe Conte said early on Sunday.
“But this is a time where we must take responsibility for ourselves.”
People are unable to enter or leave the whole northern region of Lombardy, home to 10 million people, except for emergency access. Milan is the main city in the region.
The same measures apply to 14 provinces including Venice, Parma and Modena, affecting a total of around 16 million people.
Prime Minister Conte said the provinces affected were Modena, Parma, Piacenza, Reggio Emilia, Rimini, Pesaro and Urbino, Alessandria, Asti, Novara, Verbano Cusio Ossola, Vercelli, Padua, Treviso and Venice.
Until now only around 50,000 people in northern Italy had been affected by quarantine measures.
What are the measures?
Weddings and funerals have been suspended, as well as religious and cultural events.
Cinemas, night clubs, gyms, swimming pools, museums and ski resorts have been closed.
Restaurants and cafes can open between 06:00 and 18:00 but customers must sit at least a metre apart.
People have been told to stay home as much as possible, and those who break the quarantine could face three months in jail.
Sports competitions will close to the public, and the president of Italy’s football players’ union has called for all matches to be postponed.
The plans echo China’s forced quarantine of millions of people which the WHO has praised for halting the spread of the virus.
Leading Italian politician Nicola Zingaretti said on Saturday he had tested positive for the virus.
“I am fine but I will have to stay home for the next few days,” the leader of Italy’s centre-left Democratic Party (PD) said in a Facebook post.
The country has said it will start recruiting retired doctors in an effort to combat the escalating outbreak.
Elsewhere, Iran has confirmed almost 6,000 infections and 145 deaths, and the number of cases worldwide has passed 100,000, officials say.
A second MP was reportedly among those to have died in Iran, where health officials fear the number of cases may actually be much higher.
There have so far been nearly 3,500 coronavirus deaths recorded worldwide. The majority have been in China, where the virus originated in December.
The head of the World Health Organization (WHO), Tedros Adhanom Ghebreyesus, has called the spread of the virus “deeply concerning” and urged all countries to make containment “their highest priority”.
In other developments:
- A hotel used as a coronavirus quarantine facility in the Chinese city of Quanzhou collapsed – 47 of 70 trapped people have been rescued so far
- Pope Francis is to deliver Sunday’s Angelus Prayer by livestream to avoid the usual crowds forming
- The Women’s World Ice Hockey Championships in Canada have been cancelled
- In Saudi Arabia, access to the sacred Kaaba in Islam’s holiest site Mecca remains blocked
What’s the latest on cases globally?
On Sunday South Korean officials said 367 new cases were reported in the past day, bringing the total cases in the country to 7,134.
China reported its lowest number of new infections in a single day since January.
There were 27 new deaths there from the virus, which were all in Wuhan where the outbreak began.
In Iran, 21 people are reported to have died as a result of coronavirus in the past day and more than 16,000 people are being tested in the country.
The WHO’s representative in Iran, Dr Christoph Hamelmann, said Iran was making tremendous progress at its hospitals, with facilities made available for treatment in every province.
In the US a cruise ship with 3,533 passengers and crew is being held off the coast near San Francisco after 21 people tested positive for the disease.
Washington state reported two more fatalities, bringing the the US death toll rose to 19.
In New York cases jumped from 44 on Friday to 76 and Governor Andrew Cuomo declared a state of emergency.
South America recorded its first coronavirus death, as a 64-year-old man died in Argentina.
In Australia, a man in his 80s became the third person to die there from the virus.
Among other countries to report a rise in the total number of cases are: France (to 949); Germany (795); Spain (441); the UK (206); the Netherlands (188).
Colombia, Bulgaria, Costa Rica, Malta, the Maldives and Paraguay reported their first cases.
More than 80,000 people have been infected with coronavirus in China since its emergence in the city of Wuhan, Hubei province.