Italian President Sergio Mattarella has asked outgoing Prime Minister Matteo Renzi to delay his resignation until after the budget.

Mr Renzi said he would resign after Italians voted against reforming the country's parliamentary system in a national referendum.

But Mr Mattarella said in a statement he had asked Mr Renzi to stay on until the 2017 budget has been approved by parliament, which could be as soon as Friday, to prevent emergency funding rules from kicking in on 1 January.

Once the budget has been passed, the Prime Minister can resign, the President said.

Mr Renzi, the head of the centre-left Democratic Party, has been prime minister since February 2014.

He had staked his political future on a series of major reforms to the constitution which would have concentrated the political power of lawmakers, helping streamline Italy's lengthy legislative process.

The changes, affecting about a third of the constitution, would have weakened the upper house, cut down the number of senators, and cut the powers of regional authorities.

According to the country's laws, any move to centralise power has to be put to a popular referendum in a measure designed to safeguard against a return to Mussolini-era fascism.

Mr Renzi was attacked by his opponents, including the far-right Five Star Movement, on the grounds that the reforms could be dangerous for democracy.

Italian Referendum Show all 10 1 /10 Italian Referendum Italian Referendum Italian Premier Matteo Renzi casts his ballot in a polling station during the referendum on the government's constitutional reform in Pontassieve, near Florence, Italy EPA Italian Referendum Supporters of the "No" faction for a referendum on constitutional reform hold a banner in front of Chigi palace in Rome, Italy Reuters Italian Referendum A supporter of the 'No' faction for a referendum on constitutional reform holds a flare during a protest in front of Chigi palace in Rome, Italy Reuters Italian Referendum Silvio Berlusconi after leaving Constitutional Referendum voting in Rome, Italy Rex Italian Referendum A barmaid reads the Corriere della Sera newspaper at a coffee shop in Rome, Italy Reuters Italian Referendum A man holds a banner reading 'I say no' during a march in support of the 'No' vote in the constitutional reform referendum in Rome Reuters Italian Referendum Newspaper headlines show Italian Premier Matteo Renzi's resignation following the result of Sunday's constitutional referendum, at a newsstand in Rome AP Italian Referendum An anti-referendum poster showing Premier Matteo Renzi is reflected in a scooter mirror in Rome a day after the referendum vote AP Italian Referendum Italian Premier Matteo Renzi, left, speaks during a press conference at the premier's office Chigi Palace in Rome AP Italian Referendum Italian Premier Matteo Renzi, left, leaves with his wife Agnese at the end of a press conference in Rome AP

But analysts suggested his biggest mistake was to conflate a set of complex political changes with his leadership in the eyes of the public, turning the vote into a popularity contest.

Mr Renzi said he took full responsibility for the “extraordinarily clear” defeat, with the final count showing the “No” camp winning 59.1 per cent to 40.9 per cent.