Around 16 million Italians have been quarantined under drastic government measures to try to stop the rapid spread of the coronavirus.
There was panic and confusion as the lockdown - across the entire Lombardy region and 14 provinces in four other northern regions - came into force after the number of people to test positive for COVID-19 increased by 1,247 in a single 24-hour period.
The total number of coronavirus cases in the worst affected country in Europe has jumped to from 5,883 to 7,375 - and a further 133 people have also died, taking the total number of deaths to 366.
The unprecedented decree, that affects more than a quarter of Italians, forbids anyone from leaving or entering the new red zones except for exceptional circumstances until at least 3 April.
It applies to some 10 million residents in Lombardy - which includes the financial capital Milan - 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.
The clampdown represents the most widespread effort outside of China - the origin of the deadly disease - to stop the spread of the coronavirus.
As word spread about the new restrictions on late Saturday evening, there was chaos and confusion in Padua in the Veneto region.
Packed bars and restaurants quickly emptied as scores of people rushed back to their apartments to grab their belongings and head to the railway station.
Travellers with suitcases, wearing face masks, gloves and carrying bottles of hand gel shoved their way on to trains.
Worried students wrapped scarves around their heads, shared hand sanitisers, and sat on their suitcases in the aisles on full trains.
"I read two hours ago that they may be putting out an urgent decree putting Padua in the red zone. Because I would like to return down south to my relatives, I decided to go earlier," said one student, Roberto Pagliara, heading to his hometown of Puglia in southern Italy.
Crowds also packed into the central railway station in Milan.
One student who had decided to go home to Venice earlier than he had planned, acknowledged he was heading from one red zone to another, but told Italian news agency Ansa: "I hope to be able to leave. I already have the ticket. I did not want to risk it."
Another pair of students were trying to get home to Florence. "We did not expect it," said one of the people in the lockdown, adding: "We are worried because we don't know if we will be able to leave."
"It is incredible... the infections are spreading," added another hopeful rail passenger, heading for Naples with his brother.
Local politicians reacted angrily to the measures, which were leaked to the media before regional civic leaders were alerted about the action.
The head of Lombardy, Attilio Fontano, said the proposals "go in the right direction", but were a "mess".
The head of the neighbouring Veneto region, Luca Zaia, added: "We have seen these measures at the last minute. We did not help to draw them up, and now we are being asked to give our assent almost at once. It is literally impossible."
Stefano Bonaccini, president of the Emilia Romagna region, said parts of the decree were confusing.
The mayor of Asti, in the Piedmont region, posted a video on Facebook attacking Rome for not keeping regional leaders in the loop.
"Nobody told me," wrote Maurizio Rasero, adding that he had received hundreds of messages on his mobile phone from alarmed citizens.
"It's incredible that information that is so delicate and important would come out in the newspaper first," he said.
But as southerners stranded in the north attempted to return home as soon as they could, civic leaders in the south urged them to stay put.
Michele Emiliano, the governor of Puglia, made an impassioned plea on Facebook: "I speak to you as if you were my children, my brothers, my nephews and nieces: stop and go back.
"Get off at the first train station, do not catch planes... turn your cars around, get off your buses. Do not bring the Lombard, Veneto and Emilia epidemic to Puglia."
Jole Santelli, the president of Calabria, added: "The government must block an exodus to Calabria, which risks triggering a disastrous bomb.
"Returning from the north in an uncontrolled manner endangers our land and our loved ones. Don't do it. Stop."
An estimated two million people have left southern regions and settled down in the north to further their education or in search of work.
Schools and universities remain shut down across Italy.
Measures including restricting people from visiting the elderly in nursing homes were brought in earlier this week, while older people have been urged to stay at home.
Italian Prime Minister Giuseppe Conte signed the decree just after midnight.
He said: "For Lombardy and for the other northern provinces that I have listed there will be a ban for everybody to move in and out of these territories and also within the same territory.
"Exceptions will be allowed only for proven professional needs, exceptional cases and health issues."
"We are facing a national emergency," he added. "We have to limit the spread of the virus and prevent our hospitals from being overwhelmed."
Antonio Pesenti, head of the Lombardy regional crisis response unit, told the Corriere della Sera newspaper the health system in Lombardy was "a step away from collapse".
Shops, cafes and restaurants will be allowed to stay open between the hours of 6am and 6pm - but only on condition they can guarantee customers keep to a distance of one metre between one another.
The new decree also extends closures to museums, cinemas, theatres, pubs, gyms, betting shops, spas, leisure centres and swimming pools.
Weddings and funerals have also been suspended, and holiday cancelled for all healthcare workers.
Mr Conte said the military and police forces would be responsible for ensuring the containment measures are respected and would have the powers to stop and check on those who try to move from their towns.
Meanwhile, Pope Francis gave his Sunday address via video online - instead of from a window overlooking St Peter's Square, as is tradition.
The Vatican said the move was aimed at preventing crowds gathering outside and to help stop the spread of the coronavirus, adding the Wednesday audience would be handled in the same way.
The 83-year-old Pontiff had part of one lung removed due to an illness decades ago and has cancelled most of his audiences in recent weeks.
When he appeared at the window last Sunday's blessing, he paused twice to cough. He was similarly seen coughing and blowing his nose during Ash Wednesday Mass days earlier.
A spokesperson would not confirm or deny reports the pontiff had tested negative for coronavirus, but said he was recovering from the cold and has no other pathologies.
It comes after the Vatican confirmed its first coronavirus case on Friday after a patient tested positive for COVID-19 at a clinic within the city-state.
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