“We cannot allow the efforts made to be in vain because of rashness at this delicate stage,” Conte said.
“Moving from the policy of ‘let’s close everything’ to ‘let’s reopen everything’, would risk irreversibly compromising these efforts.”
The southern region of Calabria allowed bars and restaurants with outside tables to reopen to the public on Thursday.
On Monday, the northern Veneto region – which was among the first to be hit by the virus but has suffered far fewer deaths than neighbouring Lombardy – relaxed a range of restrictions including on takeaways, pizzerias and some shops.
“Initiatives involving less restrictive measures are contrary to national rules, and are therefore to all intents and purposes illegitimate,” Conte said.
Conte on Sunday announced a gradual easing of some measures under nationwide rules beginning on May 4.
While some businesses have been allowed to reopen, the national rules remain strict.
But regional governments across Italy can set their own rules.
While local officials have previously set stricter rules that those enforced by the government, many now seem keen to reopen sooner than advised.
Evidence of a spike in infections could lead to restrictive measures being reintroduced.
Conte said officials would carry out some 150,000 tests in May to see how many people were developing antibodies to fight the virus.
He added that an app to trace contacts between potentially infected people would be voluntary.
