Italian Prime Minister Matteo Renzi is expected to be defeated in a referendum over his proposal to overhaul the constitution, three exit polls indicate.

The state broadcaster RAI's exit poll indicates that 42-46% of the voters backed the reforms put forward by Renzi while 54-58% were against them. Two other exit polls showed that the No vote had a similar lead of at least 10 points, the BBC reports.

Renzi has said that he would resign if he failed to win the referendum. He is due to make a statement at midnight (local time) from his official residence in Rome.

The turnout for the referendum has been "very high by Italian standards", the BBC said. Nearly two-thirds of the electorate had voted in prosperous northern Italy, but the voter turnout was lower in the south.

Matteo Renzi campaigns for Yes vote
Italian Prime Minister Matteo Renzi at a meeting in support of the Yes vote in the referendum in Rome, Italy, 26 November 2016 Alessandro Bianchi/Reuters