Late socialist leader Hugo Chavez’s chosen successor Nicolas Maduro won Venezuela’s presidential election by a whisker but now faces opposition protests plus a host of economic and political challenges in the Opec nation.

The 50-year-old former bus driver, whom Chavez named as his preferred heir before dying from cancer, edged out opposition challenger Henrique Capriles with 50.7 per cent of the votes in Sunday’s election, according to election board returns.

Capriles took 49.1 per cent, just 235,000 fewer ballots.

Capriles, whose strong showing confounded most forecasts, refused to recognise the result and said his team had a list of more than 3,000 irregularities ranging from gunshots to the illegal reopening of polling centres.

“I didn’t fight against a candidate today, but against the whole abuse of power,” said Capriles, the 40-year-old governor of Miranda state, demanding a recount.

“Mr Maduro, you were the loser... this system is collapsing, it’s like a castle of sand - touch it and it falls.”

A protracted election dispute could cause instability in a deeply polarised nation with the world’s largest oil reserves.

Though some opposition supporters chanted “fraud,” burned tyres, and banged pots and pans in protest, Capriles did not call them on to the streets en masse.

Maduro said he would accept a full recount, even as he insisted his victory was clean and dedicated it to Chavez.

Officials said he would be formally proclaimed winner by the election board at a ceremony and rally in downtown Caracas on Monday afternoon despite the ongoing controversy.

“I won... we’ve had a fair, legal and constitutional triumph,” Maduro told his victory rally on Sunday night, saying he would also be vigilant against destabilisation.

“We will know what to do if someone raises their insolent voice against the people.”

The election board said Maduro’s win was “irreversible” and gave no indication of when it might carry out an audit. Critics say four of its five members are openly pro-government.

Maduro’s slim victory provides an inauspicious start for the movement’s transition to a post-Chavez era, and raises the possibility he could face challenges from rivals within the coalition.