Polls have started to close in Venezuela's presidential election to determine the South American country's next leader after the death of former president Hugo Chavez last month.
Polling centres opened at 10:30 GMT on Sunday and were expected to close at 6:00pm local time (22:30 GMT).
Al Jazeera's Teresa Bo, reporting from Caracas, said some polling stations will remain open "until everyone has had a chance to vote."
According to Bo, many of supporters of Chavez's hand-picked successor Nicolas Maduro started lining up to vote in the early hours of Sunday.
"While you are here, it's impressive to see the organisation of the ruling socialist party," our correspondent said.
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of the presidential election
Lines formed under a blistering sun outside voting centres all around the capital. People stood in line outside the school where Chavez used to vote in the poor January 23 neighbourhood of the capital.
"Nicolas is going to win, but we can't afford to be triumphalist. We need to work hard to get people out to vote," said Chavista activist Mario Izarra, 33, in reference to Maduro.
In the eastern Caracas neighbourhood known as a bastion of opposition leader Henrique Capriles, voters said they were fed up.
Many cited violence that left 16,000 people dead last year and a weak economy that has people struggling to find items such as butter and milk in grocery stores.
"I want change because the situation is not good. There's no security, the country is divided in two," said Pietro Bellacicco, 75, a retired agricultural worker.
"I hope to see us united, all together again as Venezuelans."
Venezuelan residents in the US, including many who traveled by bus or flew in from Florida, lined up outside a New Orleans voting centre on Sunday to cast their ballots.
Henrique Capriles, the Venezuelan opposition candidate, called for a "true democracy" on Sunday after casting a vote.
He urged Venezuelans to report any irregularities in the election and said an "avalanche" of votes was the best answer to abuses.
"What we want is for this country to have a true democracy, a democracy for all, a country where we can all exercise our rights without the possibility of any reprisal," he said after voting in a wealthy Caracas district.
He charged that the government was sending text messages to public employees and other citizens to pressure them to vote for Maduro.
Maduro also cast his ballot in the capital. "There are very good news, turnout records are being smashed across the country," he said.
Chavez's fourth presidential election win in October last year saw record turnout of 80 percent, but this time the participation has so far been comparatively lower.
"I visited three polling stations in different parts of the city and turnout, by noon local time, seemed much lower compared to the October 2012 presidential vote," Al Jazeera's Chris Arsenault reported from Caracas.
"There doesn't seem to be a lot of energy on the streets, so far."
Nearly 19 million people are eligible to vote.
About 170 international observers were on hand for the election, many from left-leaning political parties across Latin America.
Maduro is facing off with his younger rival Henrique Capriles, governor of Miranda state, who is promising change in a polarised country.
Both camps have urged supporters to vote early and be on alert for fraud.
Trumpets sounded a reveille and fireworks exploded in Caracas in the early hours of Sunday morning, as Venezuelans were being called out to vote.
'Race not fair'
Maduro, the acting president, has said he would recognise the election results, whatever they might be.
In an interview with Teresa Bo, Capriles, who is running his second presidential campaign in less than a year, said the race had not been a fair one.
"The candidate of the government uses the presidential plane, all the military, all the ministries," he said.
This is Capriles' second presidential campaign in less than a year. In October 2012, he ran against Chavez and lost by over 10 percent. Chavez died on March 5 without being sworn into office, and another presidential election was called.
Jorge Arreaza, Venezuela's vice president, said on Friday the government had foiled a plot to destabilise Sunday's election.
Whoever wins will inherit control of the world's biggest oil reserves in an OPEC nation whose stark political polarisation is one of Chavez's many legacies. Also at stake is the generous economic aid Chavez provided to left-leaning Latin American governments from Cuba to Bolivia.
Given the deep mutual mistrust, a close or contested result could raise the chance of unrest.