"This is a difficult but necessary decision for which I take all political responsibility," Conte told a news conference.
The draconian curbs on movement and the shutdown imposed on most shops and businesses across Italy were imposed on March 9, and were scheduled to expire on Monday.
Among a few exceptions to the lockdown extension, Conte said bookshops, stationers and shops selling children's clothes could reopen from April 14.
In other remarks, he said the deal reached on Thursday among euro zone finance ministers on an economic package to help the bloc's countries is "still insufficient", adding Italy would continue to battle for the issuance of common debt through euro bonds.
