Nicolas Maduro, a former bus driver who became Hugo Chavez's protege, was declared the winner of Venezuela's presidential election on Sunday but the opposition refused to accept the result and demanded a recount of all the votes.

Opposition candidate Henrique Capriles said he did not recognise the official results that gave Maduro 50.7 per cent support versus 49.1 per cent for him, a difference of just 235,000 ballots.

"Maduro, if you were illegitimate before, now you are even more loaded with illegitimacy," Capriles said, adding that his team had identified more than 3,000 "incidents" during the voting.

Capriles' refusal to accept the result raised fears of political unrest in Venezuela, an Opec nation with the world's biggest oil reserves.

The National Electoral Council earlier said that more than 99 per cent of votes had been counted and that Maduro's victory was "irreversible."

Government supporters immediately gathered to celebrate outside the Miraflores presidential palace, where Maduro paid an emotional tribute to Chavez, the socialist leader who named him as his successor in his last speech to the nation before dying last month from cancer.

"The fight continues!" Maduro, 50, told the victory rally.

"This was the first time without the giant candidate, but he left behind his 'son,' who is now going to be president and is going to show he is worthy of the fatherland."

Some opposition supporters in Caracas banged pots and pans in protest as Maduro spoke. – Reuters