Big businesses such as factories can remain open as long as they adopt “appropriate security measures to prevent contagion,” Conte said.
Conte asked people to stay indoors unless they need to buy food or other necessities.
People are also allowed to leave the house and travel to work, if their employer has not put them on leave or allowed remote working.
Conte did not announce any new restriction on transport in the address. He said essential public services, including public transport and utilities, are “guaranteed”.
The Italian leader stressed in his nine-minute evening prime time address that there was “no need to rush to buy groceries” because food stores would stay open throughout.
Italians have watched ever-tighter restrictions slowly eat away at the very fabric of everyday life since the weekend.
An existing clampdown on public gathering and basic travel had already emptied streets and shuttered everything from churches to gyms and cinemas.
Cathedrals on Tuesday posted hand-written notes cancelling mass and cafes apologised to their regulars for having to turn them away.
Conte said the closure of nearly everything that had remained open under the previous restrictions would run for at least two weeks.
“Thank you to all Italians who make sacrifices. We are proving to be a great nation,” Conte said in his nine-minute evening prime time address to the nation.
He told Italians: “Just a few days ago I asked you to change your habits and stay at home, and you have responded in an extraordinary way.”
You are making enormous sacrifices, I know that’s not easy, but these are making a great and precious contribution to the country. The whole world is watching us, especially watching the number of cases.”
Overall in Italy, 827 people have now died from the COVID-19 disease caused by the virus and more than 12,000 have been infected in just under three weeks since the outbreak began in northern Italy.
This figure includes the deceased and a total of 1,045 people who have now recovered – 40 more then on Tuesday.
This means the total number of active cases in Italy is now at 10,590.
There are now over a thousand patients in intensive care nationwide – 560 of these are in the Lombardy region alone, where hospitals are struggling to cope.
The northern region of Lombardy is by far the worst-hit part of Italy. It has also seen most of the deaths with 617 in total as of Wednesday.
The region of Emilia-Romagna has had 113 fatalities and Veneto in the north east 29.
The vast majority of the deaths have been in northern Italy, though the southern region of Puglia has now recorded five deaths, and Campania on Wednesday recorded its first fatality.
Find all The Local's coverage of the coronavirus outbreak in Italy here.