Colombians are going to the polls to decide whether to approve a peace deal with the country's largest rebel movement.
Polls taken before Sunday's referendum - in which voters are being asked whether they want to ratify or reject a deal ending decades of hostilities with the Revolutionary Armed Forces of Colombia (Farc) - show the "yes" vote favoured by an almost two-to-one margin.
Government ministers said they were not taking victory for granted after a highly-polarised campaign that has exposed how steep a challenge it faces implementing the 297-page accord and bringing about real reconciliation.
Colombians overwhelmingly loathe the Farc, which the US considers a terrorist group, and many consider provisions in the accord that would spare the rebels jail time an insult to the 220,000 killed and almost eight million displaced by the long-running conflict.
In the past month, ever since the deal was announced in Cuba after four years of negotiations, the government has spent heavily on television ads and staged concerts and peace rallies around the country to get out the vote.
For the first time in an election, it is making ballots available in Braille so blind Colombians can vote.
"We don't want anyone to be feeling excluded because this is an important decision," said Luisa Fernanda Morena, a 30-year-old volunteer preparing the materials at the National Institute for the Blind.
For the referendum to be ratified, at least 13% of the electorate, or 4.5 million voters, must cast "yes" ballots.
Turnout is expected to be low, no higher than the 40% seen in recent congressional elections, a sign to some analysts that Colombians' enthusiasm for the ambitious accord is lacking.
Also potentially affecting turnout, especially along the Caribbean coast, is heavy rainfall left by Hurricane Matthew, which has been parked off the northern tip of South America since Friday.
President Juan Manuel Santos urged his compatriots to vote early and take inspiration from Indian independence leader Mahatma Gandhi.
"We in Colombia have to adopt this culture of non-violence," Mr Santos said shortly after casting his ballot in a washed-out Plaza Bolivar next to the presidential palace.
"All of us can be protagonists in this historic change taking place in our nation."
The opposition, led by ex-president Alvaro Uribe, argues the government is appeasing Farc and setting a bad example that criminal gangs will seize on.
If the "no" vote were to prevail, Mr Uribe said the government should return to the negotiating table, an option both Mr Santos and Farc have ruled out.
In recent days, Farc have made an effort to show its commitment to peace is real.
Twice this week leaders of the group travelled to areas hard hit by the violence to apologise for massacres committed by their troops and discuss with communities how they can compensate victims.
"All of us in life have committed mistakes, some with consequences more serious than others," Farc leader Ivan Marquez said on Friday at a ceremony in a northern Colombian town where rebels in 1994 disrupted a street party with gunfire, killing 35.