Hugo Chávez appeals for peace on the eve of the Venezuelan presidential election. Link to this videoVenezuelan voters will get the chance to have their say on the rule of Hugo Chávez as polls open on Sunday in the most closely fought presidential election since the former tank commander won power in 1998.

Most opinion polls suggest the president will be re-elected, albeit by a substantially reduced margin from his previous landslide victories. But the large number of undecided voters and strong turnouts at opposition rallies have given late momentum to the challenger, Henrique Capriles, who has a genuine chance of an upset.

With Venezuela sitting on the world’s largest oil reserves and Chávez a leading figure in the resurgence of the political left in Latin America, the vote will have an impact on the global economy, energy supplies and regional geopolitics.

But for most of the country’s almost 19m voters, the key concerns are the alarming rise in the murder rate, the redistribution of oil wealth and the personality and health of the man who has led them for the past 13 years.

Chávez – who was due to vote during the morning in the revolutionary stronghold of the 23 de Enero barrio – has called his challenger a candidate from the extreme right and warned that “all the country could lose, even the rich” if there were a change of government.

“The middle classes should vote for Chávez because we are a guarantee of stability, peace, national development”, he said in a recent broadcast. In contrast, Capriles – who was scheduled to cast his ballot soon after noon in an upmarket neighbourhood of west Caracas – has tried to present himself as a centrist who can unify the nation. Declaring himself a David facing a Goliath, he has described Chávez as a formidable contender and promised to continue his poverty relief programs.

Poll predictions have ranged from a 25-point landslide for Chávez to a six-point win for Capriles. With the president debilitated by an almost year-long battle with cancer, the recent momentum appears to have been with the opposition. It will not be clear until late on Sunday whether it has done enough to close the ground on one of the most charismatic and controversial campaigners in Latin American history.

Both camps predict victory but have said they will accept the results, whatever the outcome. However, analysts fear a narrow win for either side could spark accusations of fraud and street violence. This has put the voting system under intense scrutiny, but it appears robust. External observers and domestic analysts have lauded the procedure as one of the most sophisticated systems in the world.

Voters first register themselves by inputting their name, national identity number and thumbprint into a console. They then cast an electronic vote for their preferred party candidate on a touchscreen. Their vote enters the central counting system and is also printed so that they can confirm that it has been recorded properly before putting this hard copy in a ballot box – more than half the contents of which will later be cross-checked with the electronic data to ensure the system has not been hacked.

Voters must then sign a form to confirm they have cast a vote. Before they leave, the little finger on their left hand is marked with indelible purple ink so they cannot return to vote a second time.

“This system is 100% fraud proof and has been recognised as such by outside political institutions,” said Luis Guillermo Piedra, of the National Electoral Council.

Former US president Jimmy Carter has described the system as superior to that of the US. His Carter Centre, based in Atlanta, Georgia, has noted that many Venezuelans are concerned that a new electronic voting system might enable authorities to tell how they voted, exposing them to retaliation if they vote against Chávez. “This concern has no basis, however,” the centre said. “The software of the voting machines guarantees the secrecy of the vote.”

There is less certainty about what happens outside the voting booths. The opposition have lodged 110 complaints about alleged abuses of election laws by the Chávez campaign, mostly relating to his domination of airtime on public broadcasting channels and use of funds, staff and other resources from state-owned enterprises. They also fear that armed militias may put pressure on voters before they go to the polls, though there have been no reports of this to date.