Chavez retains a devoted following among the country's poor, who have propelled him to easy victories in past elections, but Capriles narrowed the gap in opinion polls after an energetic door-to-door national campaign.
"I've been here since 2:00 am in order to vote to continue what we have achieved so far," said Richard Lozano, who stood in line at polling station in the sprawling Petare slum.
Experts say the electronic voting system is reliable and all candidates have signed a pledge to accept the result. But Chavez charges that the "far right" plans to not recognise his victory if he wins. "I call on all political actors from the left, right and centre for us to prepare emotionally to accept" the result, Chavez said.