Italy has ordered a virtual lockdown across much of its wealthy north, including the financial capital Milan, in a drastic new attempt to try to contain the coronavirus outbreak.

The unprecedented restrictions, which aim to limit gatherings and curb movement, will impact some 16 million people and stay in force until April 3.

They were signed into law overnight on Sunday (local time) by Prime Minister Giuseppe Conte.

The new measures say people should not enter or leave Lombardy, Italy’s richest region, as well as 14 provinces in four other regions, including the cities of Venice, Modena, Parma, Piacenza, Reggio Emilia and Rimini.

Only people with proven, work-related reasons, or health problems will be able to move in and out of the exclusion zones. Leave has been cancelled for health workers.

“We are facing a national emergency. We chose from the beginning to take the line of truth and transparency and now we’re moving with lucidity and courage, with firmness and determination,” Mr Conte said.

“We have to limit the spread of the virus and prevent our hospitals from being overwhelmed,” he told a news conference.

The number of coronavirus cases in the country jumped 25 per cent in a 24-hour period to 7375, while deaths climbed 57 per cent to 366 deaths.

It was the largest daily increase for both readings since the contagion came to light on February 21.

A lockdown was signed into law overnight on Sunday by Prime Minister Giuseppe Conte. Photo: Getty

Head of the Lombardy regional crisis response unit Antonio Pesenti told the Corriere della Sera newspaper the health system in Lombardy was “a step away from collapse”.

“We’re now being forced to set up intensive care treatment in corridors, in operating theatres, in recovery rooms. We’ve emptied entire hospital sections to make space for seriously sick people,” he said.

The Milan stock exchange, whose all-share index has plunged 17 per cent since the crisis broke, was scheduled to open normally on Monday but one trader said he expected “a violent sell-off” as markets digested the lockdown of Italy’s economic heartland.

Healthcare professionals with an elderly patient at the hospital of Schiavonia, northern Italy. Photo: AAP

The World Health Organisation said it fully supported the actions taken by Italy, which were in line with its guidelines for containing the spread of the virus.

But with the Italian economy already on the edge of recession, some local politicians pushed back against the measures, which leaked out before the regions were consulted.

Veneto head Luca Zaia complained he had not been properly consulted and was unhappy that three provinces in his region, including Venice, had been included in the clampdown.

“We do not understand the rationale of a measure that appears scientifically disproportionate to the epidemiological trend,” he wrote on Facebook.

On Saturday, health officials had expressed alarm at the apparent lack of concern in the general public, as fine weekend weather attracted large crowds to the ski slopes outside Milan.

But streets were notably quieter than normal as northern cities woke up to the news on Sunday.