Over 15 million people across a vast swathe of northern Italy woke on Sunday to find themselves cut off from the rest of the country, after the government imposed a virtual lockdown to prevent the coronavirus spreading.

Prime Minister Giuseppe Conte signed off on plans that strictly limit movement in and out of the north, including Venice and the financial capital Milan, for nearly a month.

"The virus closes the heart of the north," the Stampa daily's headline read, while Il Messaggero went with "Half of Italy shuts".

It was not clear however how strictly the order would be enforced, or how authorities could prevent people from leaving.

The decree said that only people with a "serious" reason that cannot be postponed, such as urgent work or family issues, would be allowed in or out of the quarantine zones, which affect a quarter of Italy's population of 60 million.

But it does allow for the return home of those who were in the affected areas but live elsewhere, including tourists.

Flights appeared to be operating normally out of Milan and Venice airports, while it was business as usual at train stations.

Streets in Milan were largely deserted.

With more than 230 fatalities, Italy has recorded the most deaths from the COVID-19 disease of any country outside China, where the outbreak began in December.

The new rules came shortly after the news the number of people infected had jumped by over 1,200 in a 24-hour period.

'Uncertainty, anxiety, confusion'

The plan was leaked to the media Saturday, infuriating Conte, who slammed it as "unacceptable", saying it had created "uncertainty, anxiety, (and) confusion".

Italian virologist Roberto Burioni described the leak Sunday on Twitter as "pure madness".

"The draft of a very harsh decree is leaked, sparking panic and prompting people to try and flee the (then) theoretical red zone, carrying the virus with them," he said on social media.

"In the end, the only effect is to help the virus to spread. I'm lost for words".

The virus has now spread to all 22 Italian regions and the first deaths are being recorded in Italy's less well medically equipped south.

'Turn around'

The head of the Puglia region in southern Italy pleaded with anyone thinking of returning from Lombardy and the other 11 provinces in lockdown -- which include the cities of Parma and Rimini -- to "stop and turn around".

"I'm speaking to you as if you were my children, my brothers, my grandchildren," he said on Facebook.

"Get off (the train) at the first station, don't get on the flights to Bari and Brindisi, turn your cars around, get off the bus at the next stop. Don't bring the epidemic to Puglia.

"You are carrying to the lungs of your brothers and sisters, grandparents, uncles, cousins, and parents, the virus that has severely strained the health system in northern Italy," he said.

Anyone making the journey anyway would be placed in obligatory quarantine for 14 days, he said.

Italy has found itself at the forefront of the global fight against the virus, with more than 5,800 infections recorded in the past seven weeks.