Venezuela's opposition and President Nicolas Maduro's government were locked in a high-stakes standoff after each side claimed victory in Sunday's presidential vote, which millions in the long-suffering nation saw as their best shot to end 25 years of single-party rule.

Several foreign governments, including the U.S., held off recognizing the results as election officials delayed releasing detailed vote tallies after proclaiming Maduro the winner with 51 per cent of the vote, to 44 per cent for retired diplomat Edmundo Gonzalez.

"Venezuelans and the entire world know what happened," Gonzalez said.

U.S. Secretary of State Antony Blinken from Tokyo said the U.S. has "serious concerns that the result announced does not reflect the will or the votes of the Venezuelan people."

Gabriel Boric, the leftist leader of Chile, said: "The Maduro regime should understand that the results it published are difficult to believe."

Meanwhile, on the streets of Caracas, a mix of anger, tears and loud pot banging greeted the announcement of results by the Maduro-controlled National Electoral Council.

"This isn't possible," said Ayari Padron, wiping away tears. "This is a humiliation."

Lines to vote began at dawn

Voters lined up before dawn to cast ballots Sunday, boosting the opposition's hopes it was about to break Maduro's grip on power.

The official results came as a shock to opposition members who had celebrated, online and outside a few voting centres, what they believed was a landslide victory for Gonzalez.

"I'm so happy," said Merling Fernandez, a 31-year-old bank employee, as a representative for the opposition campaign walked out of one voting centre in a working class neighbourhood of Caracas to announce results showing Gonzalez more than doubled Maduro's vote count. Dozens standing nearby erupted in an impromptu rendition of the national anthem.

"This is the path toward a new Venezuela," added Fernandez, holding back tears. "We are all tired of this yoke."

Opposition leader Maria Corina Machado said the margin of Gonzalez's victory was "overwhelming," based on voting tallies the campaign received from representatives stationed at about 40 per cent of ballot boxes.

Authorities delayed releasing the results from each of the 30,000 polling booths nationwide, promising only to do so in the "coming hours," hampering attempts to verify the results.

Opposition candidate blocked from running

Gonzalez was the unlikeliest of opposition standard bearers. A retired diplomat, the 74-year-old was unknown until he was tapped in April as a last-minute stand in for opposition powerhouse Machado, who was blocked by the Maduro-controlled supreme court from running for any office for 15 years.

The delay in announcing a winner — which came six hours after polls were supposed to close — indicated a deep debate inside the government about how to proceed after Maduro's opponents came out early in the evening all but claiming victory.

After finally claiming to have won, Maduro accused unidentified foreign enemies of trying to hack the voting system.

"This is not the first time that they have tried to violate the peace of the republic," he said to a few hundred supporters at the presidential palace. He provided no evidence to back the claim but promised "justice" for those who try to stir violence in Venezuela.

The election will have ripple effects throughout the Americas, with government opponents and supporters alike signalling their interest in joining the exodus of 7.7 million Venezuelans who have already left their homes for opportunities abroad should Maduro win another six-year term.

Authorities set Sunday's election to coincide with what would have been the 70th birthday of former president Hugo Chavez, the revered leftist firebrand who died of cancer in 2013, leaving his Bolivarian Revolution in the hands of Maduro. But Maduro and his United Socialist Party of Venezuela are more unpopular than ever among many voters who blame his policies for crushing wages, spurring hunger, crippling the oil industry and separating families due to migration.

The opposition managed to line up behind a single candidate after years of intra-party divisions and election boycotts that torpedoed their ambitions to topple the ruling party.

A former lawmaker, Machado swept the opposition's October primary with over 90 per cent of the vote. After she was blocked from joining the presidential race, she chose a college professor as her substitute on the ballot, but the National Electoral Council also barred her from registering. That's when Gonzalez, a political newcomer, was chosen.

Soaring inflation

Venezuela sits atop the world's largest proven oil reserves, and once boasted Latin America's most advanced economy. But it entered into a free fall after Maduro took the helm. Plummeting oil prices, widespread shortages and hyperinflation that soared past 130,000 per cent led first to social unrest and then mass emigration.

Economic sanctions from the U.S. seeking to force Maduro from power after his 2018 re-election — which the U.S. and dozens of other countries condemned as illegitimate — only deepened the crisis.

Maduro's pitch to voters this election was one of economic security, which he tried to sell with stories of entrepreneurship and references to a stable currency exchange and lower inflation rates. The International Monetary Fund forecasts the economy will grow four per cent this year — one of the fastest in Latin America — after having shrunk 71 per cent from 2012 to 2020.

But most Venezuelans have not seen any improvement in their quality of life. Many earn under $200 a month, which means families struggle to afford essential items. Some work second and third jobs. A basket of basic staples — sufficient to feed a family of four for a month — costs an estimated $385.

The opposition has tried to seize on the huge inequalities arising from the crisis, during which Venezuelans abandoned their country's currency, the bolivar, for the U.S. dollar.