A majority of Italians abroad voted to express support for the failed constitutional reform proposals pushed by Matteo Renzi, final figures have revealed.

Ministry of Internal Affairs figures show almost 65 per cent of Italians living or working abroad backed the outgoing Prime Minister's plan - a result that is the opposite of the overall outcome in the country.

The overall 'No' vote led 'Yes' by almost 20 points, pushing Mr Renzi to announce his resignation only one hour after polls had closed, with counting still under way.

As well as paving the way for the possibility of an early election, Mr Renzi’s resignation sparked concerns a deep political crisis might be inevitable, as the country could go to the polls as early as next year.

About four million Italians living abroad were eligible to vote in Sunday's referendum through a postal ballot, and turnout, at about 30 per cent, was consistent with figures from past elections.

In South America, where Italians eligible to vote total about one million people, 'Yes' led 'No' by a margin of about 44 per cent.

Brazil and Argentina, which are part of one larger electoral college, have substantial populations of Italian ancestry. Throughout the years, both countries welcomed several waves of mass migration from Italy, and descendants retain Italian citizenship and the right to vote in Italian elections through the right of blood.

'Yes' led 'No' by about 25 points in North America, Central America, and Europe. The margin narrows for votes counted in Africa, Asia, and Oceania, where the votes cast for 'Yes' totalled about 59%.

'No' led 'Yes' in some Eastern European countries, including Bulgaria, and Russia, where 'No' led 'Yes' by about 13 points. 'No' also won in Japan, Iceland, and the United Arab Emirates, among other countries.

Of the 232,932 Italian voters registered in the UK, 37,60 per cent cast a ballot to vote in Sunday’s referendum, with 'Yes' leading 'No' by 25 points.

“I voted 'Yes' because I think Italy has a problem with paralysis and slowness in decision making”, Mauro Terrinoni, a 41 year-old London-based entrepreneur from Italy, said, adding that he had followed ”the reform proposals from the beginning” and had “always wanted to vote 'Yes'”.

According to Mr Terrinoni, more accountability and a faster decision-making process are required, and Mr Renzi’s constitutional reform would have brought about change in that direction.

Voting for Italians who live abroad has been a right since 2001, when late centre-right Minister Mirko Tremaglia pushed for a law regulating the matter.