Hondurans vote for a successor to deeply unpopular President Juan Orlando Hernandez in elections that could oust his National Party after 12 years in power.
Hondurans voting in what electoral officials said were "massive" numbers has boosted opposition hopes of ending a dozen years of National Party rule and possibly paving the way for leftist Xiomara Castro to win the presidency.
If she wins Sunday's election, opposition standard-bearer Castro would become the first female president in Honduras and mark the left's return to power for the first time since her husband, former president Manuel Zelaya, was deposed in a 2009 coup.
As polls closed, the electoral council said more than 2.7 million voters had already cast ballots, a figure the council described as a "massive turnout" but with more votes yet to be counted.
Council president Kelvin Aguirre said it had already surpassed total turnout four years ago.
He added that voters still in line could vote, in a contest marked by efforts from the conservative ruling party to shake off numerous corruption scandals while attacking Castro as a dangerous radical.
Long lines could be seen at many polling places across the capital. Nationwide, some 5.2 million Hondurans are eligible to vote.
'It's now or never'
For months, Castro has sought to unify the opposition to outgoing President Juan Orlando Hernandez, who has denied accusations of having ties to powerful gangs, despite an open investigation in the United States allegedly linking him to drug trafficking.
After tying up with the 2017 runner-up, a popular TV host, most polls have reinforced her front-runner status.
"We can't stay home. This is our moment. This is the moment to kick out the dictatorship," said Castro, mobbed by reporters just after voting in the town of Catacamas earlier in the day.
"It's now or never."
But such is the level of mistrust among Hondurans in the electoral process that many fear there could be disturbances in the streets no matter who wins.
Latest political flashpoint
The election is the latest political flashpoint in Central America, a major source of US-bound migrants fleeing chronic unemployment and gangland violence.
The vote also has prompted diplomatic jostling between Beijing and Washington after Castro said she would open diplomatic relations with China, de-emphasising ties with US-backed Taiwan.
Castro's main rival among 13 presidential hopefuls on the ballot is the National Party's Nasry Asfura, a wealthy businessman and two-term mayor of the capital Tegucigalpa, who has tried to distance himself from the unpopular incumbent.
After casting his ballot, a measured Asfura said he would respect voters' verdict.
Observers see calm voting with high turnout
Numerous national and international election observers monitored Sunday's voting, including the European Union's 68-member mission.
Zeljana Zovko, the EU's chief observer, told a scrum of reporters around midday that her team mostly saw calm voting with high turnout, although most polling stations they visited opened late.
On Sunday afternoon, National Party leader Fernando Anduray declared an Asfura win while voting continued.
In addition to the presidential race, voters are also deciding the composition of the country's 128-member Congress, plus officials for some 300 local governments.
Preliminary results are expected around 9 pm [local time].