President and one-time Sandinista revolutionary Daniel Ortega is headed for a mandate to stay in office in Nicaragua, overcoming a constitutional limit on re-election and reports of voting problems.

Ortega had 64 per cent of the votes in a count early Monday, compared with 29 per cent for his nearest challenger, Fabio Gadea. Conservative Arnoldo Aleman, a former president, was a distant third with six per cent after national elections on Sunday.

Only 16 per cent of the votes have been counted, but electoral council President Roberto Rivas said a quick count representative of the entire vote gave Ortega a large advantage as well. The methodology of the quick count was not released.

International election observers reported problems with access to voting stations. One national group of observers, Let's Have Democracy, said it recorded 600 complaints of voting irregularities, a handful of injuries in protests and 30 arrests.

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Nicaragua's President, Daniel Ortega, raises his ballot before casting his vote at a polling station on Sunday. (Esteban Felix/Associated Press)

A team from the European Union said it would issue a report Tuesday after investigating all the complaints, which included a polling place set on fire, election officials obstructing voters from opposing parties and protests by those who didn't receive their voting credentials.

The head of the Organization of American States observer mission, Dante Caputo, initially complained that its observers were been denied access to 10 polling stations, but later said in a statement that the issue was resolved.

He said that the OAS team didn't see "significant irregularities" but urged authorities to investigate all the complaints.

Claims of widespread fraud in the 2008 municipal elections led Washington to cancel $63 million Cdn in development aid.

Ortega had yet to acknowledge a victory early Monday, though he had already received congratulations from his leftist allies, Cuban President Raul Castro and Venezuelan President Hugo Chavez, who has given the Ortega government more than $509 million a year in donations and discounted oil.

The ruling Sandinista party declared victory and caravans of thousands of supporters flooded the streets shouting "Daniel! Daniel!"

Since returning to power in 2007, the 65-year-old Ortega has boosted his popularity in Central America's poorest country with a combination of pork-barrel populism and support for the free-market economy he once opposed.

Ortega seeking third term

He was running for a third term — his second consecutive one — after the Sandinista majority on the Supreme Court overruled the term limits set by the Nicaraguan constitution.

His opponents feared that if he wins more than 50 per cent of the vote, it would allow him to change the constitution to legitimize the Supreme Court ruling and pave the way to becoming president for life.

Ortega has dismissed such charges as scare tactics from his enemies, and said the results would indicate the Nicaraguans are now voting "without fear."

Ortega had been seeking a clear majority after winning in 2006 with only 38 per cent of the vote.

He led the Sandinista movement that overthrew dictator Anastasio Somoza in 1979, and withstood a concerted effort by the U.S. government, which viewed him as a Soviet-backed threat, to oust him through a rebel force called the Contras.

The fiery, mustachioed leftist ruled through a junta, then was elected in 1984 but was defeated after one term in 1990. He lost again in 1996 and 2001 despite garnering more than 40 per cent of the vote.

A constitutional move lowering the percentage required to win a presidential election from 45 to 35 helped his victory in 2006, despite a divided vote.