Italian Prime Minister Renzi has announced his intention to resign following a defeat in a referendum over his plan to reform the constitution.
Mr Renzi made the announcement at a press conference during which he said he accepted full responsibility for the defeat.
A projection by the Piepoli Institute/IPR for state broadcaster RAI, estimated those voting 'Yes' to back the reform at 39-43%, compared with 57-61% for 'No'.
Polls for national broadcaster Rai and the La7 television channel both gave the No camp as winners by a margin of at least 54% to 46% in this evening's referendum.
The euro immediately fell against the dollar on the exit polls, slipping to $1.0580 from $1.0625.
The result will represent a fresh blow to the European Union which is struggling to overcome an array of crises and was eager for Mr Renzi to continue his reform drive in the eurozone's heavily indebted, third-largest economy.
About 51 million Italians were eligible to vote on Mr Renzi's plan to drastically reduce the role of the upper house Senate and claw back powers from regional authorities.
Full results are not due until at least 2am.
Defeat could also prompt fresh market ructions, especially in the banking sector which has lost almost half its value this year on the Milan bourse, hit by fears over its huge exposure to bad loans accumulated during years of economic downturn.
Mr Renzi, 41, took office in 2014 promising to shake up Italy and presenting himself as an anti-establishment "demolition man" determined to crash through a smothering bureaucracy and redraw the nation's creaking institutions.
Marine Le Pen says Italians have "rejected the EU" (and Renzi) in her first response to the Italian referendum on constitutional reform. https://t.co/iHXLoeNMB6
— Tony Connelly (@tconnellyRTE) December 4, 2016
Today's referendum, designed to hasten the legislative process by reducing the powers of the upper house Senate and regional authorities, was to have been his crowning achievement.
However, his reforms so far have made little impact and the opposition 5-Star Movement has claimed the anti-establishment banner, tapping into a populist mood that saw Britons vote to leave the European Union and Americans elect Donald Trump president.
Under Italian law, Mr Renzi had to call a referendum on his plans to overhaul the constitution, but it was his decision to pin his future to the outcome, arguing that if Italy was not willing to accept his recipe for change he should leave office.
This move turned the vote into a de facto plebiscite on Mr Renzi himself, uniting disparate opposition forces in a fierce battle to unseat Italy's youngest prime minister that played out over months of relentless campaigning.
