Exit polls in Ecuador suggest voters have strongly backed President Rafael Correa's plans for a fundamental overhaul of the political system.
Many voters say they do not fully understand the proposals
A poll showed 78% support for a people's assembly that would by-pass Congress and rewrite the constitution.
Mr Correa says reform of the system is essential but his critics accuse him of being authoritarian.
Counting is expected to be a long process and official results will not be available for a number of days.
However, the BBC's Daniel Schweimler in Quito says supporters of President Correa were out on the streets just minutes after polling stations closed at 2200 GMT.
He was shown on national television celebrating at a hotel in the country's largest city, Guayaquil.
A CEDATOS-Gallup exit poll of 40,000 voters nationwide showed 78% in favour and 11.5% opposed.
The debate had turned personal with critics of President Correa making accusations of drug-running in his family.
Mr Correa admitted his father was arrested for carrying drugs into the US 40 years ago.
But he said: "I lived through this and these people are not delinquents. They are single mothers or unemployed people who are desperate to feed their families."
Many of his critics have accused him of trying to increase his power and following in the footsteps of President Hugo Chavez who has brought in controversial reforms in Venezuela.
Former Ecuador president Oswaldo Hurtado said of the referendum: "It's not a project for a better democracy. It's a project to accumulate power. All dictators always have had constitutions made to fit them."
Mr Correa has not spelt out exactly what he wants from a new constitution but has indicated that Congress, controlled by traditional political parties, should not appoint judges and electoral officials.
The assembly would be elected within three months and have six months to draft the constitution. The document would then be put to a second referendum.
President Correa has said he is confident of victory
"It will be a constitution that depoliticises the courts and control authorities, decentralises the state," Mr Correa said, adding he would quit and "go home" if there was a "no" vote.
Daniel Schweimler says President Correa is taking a bold gamble in a country that has seen eight presidents in the past 10 years.
But our correspondent says the political system in Ecuador is fragile and the president believes only radical measures will win back the people's faith in their politicians.
International monitors said the referendum was well prepared.
Ahead of voting, it had sparked a political crisis in the country.
An electoral court sacked 57 lawmakers in March for trying to block it.
When the dismissals were ruled illegal, police prevented the legislators returning to their offices and the deputies were kicked and punched by Correa supporters.