Blanket travel restrictions were announced on Sunday for Italy’s Lombardy region and 14 more provinces.
These restrictions will now be put in place across the rest of the country, as well as a ban on all public events.
Conte said people will only be allowed to travel for work or family emergencies in order to protect the most fragile members of society from the virus.
Schools and universities across the country will be closed until 3 April, but Conte said public transit will remain operational.
Passengers departing on flights who are not temporary visitors will have to justify their travel, as will people arriving by plane.
There will be controls at train stations to check temperatures, and cruise ships will be forbidden to dock at various ports.
More than 400 people have died from COVID-19 in Italy, and there are 9,172 cases.
Italy has the most cases of the novel coronavirus of any European country, with cases confirmed in all 20 regions.
The lockdown in the north saw inmates overrun numerous prisons on Monday in response to visitors being banned to prevent further spread of the virus.
The uproar resulted in prisoners escaping their facilities and kidnapping officers across 22 prisons.
