(Adds results, reaction)
By Eyanir Chinea and Andrew Cawthorne
CARACAS, Dec 10 (Reuters) - President Nicolas Maduro's socialist government was on course to sweep Venezuela's nationwide mayoral elections on Sunday, deepening opposition disarray and strengthening his hand ahead of a likely 2018 re-election campaign.
With three of the main opposition parties boycotting the polls, Maduro said the ruling Socialist Party took at least 90 percent of the 335 mayorships in the OPEC nation that is suffering an unprecedented economic meltdown.
"I'm so happy for our great victory,," a beaming and dancing Maduro, 55, told a crowd in Plaza Bolivar in the capital Caracas. "Now let's get ready for 2018!"
According to the national election board's latest official count, the socialists had won 41 of 42 mayorships counted by late evening. But Maduro said the results overnight would show his government had won more than 300 of the total 335 polls.
Opposition parties, who boycotted the polls accusing the election board of bias towards Maduro's "dictatorship", said Sunday's election was - like others - full of irregularities including flagrant abuse of state resources.
"What happened today wasn't an election, and no one will see it as such," said the hardline opposition party Popular Will. "Venezuelans want to vote in free and fair conditions."
Maduro said the three abstentionist opposition parties - Popular Will, Justice First and Democratic Action parties - should be not be allowed to participate in future votes.
"They will disappear from the political map," said Maduro, now favorite to be the Socialist Party's candidate next year.
There is speculation the pro-Maduro election board may call the presidential poll for the first half of 2018, though it has traditionally been held in December. That would give the opposition a short window to unite and raise shattered morale.
With its most popular leaders barred in advance - Leopoldo Lopez is under house arrest and Henrique Capriles is prohibited from office - it may struggle to find a popular flagbearer.
Some more moderate parties in the disparate opposition coalition did run candidates on Sunday. That confused grassroots opposition supporters already despondent over the failure to weaken Maduro in months of protests earlier this year that turned violent and resulted in 125 deaths.
ECONOMIC CRISIS
Under Maduro's rule since 2013, Venezuela has endured one of the worst economic meltdowns in Latin American history, with millions skipping meals, struggling to find medicines and reeling from the world's highest inflation rate.