State elections will determine opposition leader Capriles's future ahead of possible new presidential vote if Hugo Chavez is incapacitated by cancer.
The vote for 23 state governorships, seven of which are currently controlled by the opposition, has been overshadowed by the president's battle to recover from cancer surgery in Cuba.
Henrique Capriles (40) needs to hold on to the governorship of Miranda state to remain the opposition's presidential candidate-in-waiting, while both sides will want a good showing to create momentum in case of a new showdown over who replaces Chávez.
"This is the best indication of how well the opposition will fare in an upcoming contest for the presidency between Henrique Capriles and designated Chávez dauphin vice-president Nicolas Maduro," said Russell Dallen of Caracas-based BBO Financial Services.
Turnout was thin in early voting across the country, in contrast to the long lines for the presidential ballot two months ago, which handed Chávez a third term.
"I'm surprised. In the presidential election I got here at 3am and there were a lot of people in line. Today I got here at 5am and I was the first person," said Nathaly Betancourt, who was voting in the western city of Punto Fijo.
Empty voting centres
Opposition sympathisers complained via Twitter that centres in affluent anti-Chávez sectors of Caracas that are crucial for Capriles were notably empty.
The South American Organisation of the Petroleum Exporting Countries nation appears more focused on Chávez's recovery in Havana from Tuesday's operation – the socialist leader's fourth since he was diagnosed with cancer in his pelvic region in mid-2011.
Government officials on Saturday night said Chávez had regained full consciousness and was giving instructions. His son-in-law, who serves as science and technology minister, acknowledged there had been "moments of tension" during and after the operation, but said Chávez was steadily improving.
Few medical details have been released, so speculation remains rife that Chávez may be in a life-threatening situation in Havana's Cimeq hospital with both a difficult post-operative recovery and a possible spreading of the cancer.
Chávez (58) is due to start a new term on January 10, but has named Maduro as his preferred successor should he be incapacitated. That would trigger a new presidential poll within 30 days.
Chávez's illness has led to an outpouring of emotion including Catholic masses, prayer meetings and vigils across the country.
Maduro has wept in public, state media are replaying images of Chávez round-the-clock and various government candidates held closing rallies simply playing the president's voice.
The sympathy factor could benefit Chávez's candidates and offset the disadvantage of losing his charismatic presence on the campaign trail in advance.
"Without wishing to be triumphalist, we have big chances of winning the 23 governorships and that is the biggest support we can give Chávez," said his brother Adán Chávez, who is seeking re-election in their home state of Barinas.
Still smarting from defeat in October, the opposition hopes voters will focus on grassroots issues and punish the government for power outages, pot-hole riddled roads, corruption scandals, violent crime and runaway inflation.
"I put my life at the service of Miranda and Venezuela," Capriles said in his closing rally. "I'm not here to stay in power but to make a dream [of national change] come true."
Though widely expected to retain his Miranda seat, Capriles faces a well-financed challenge from senior Chávez ally Elias Jaua – a former vice-president. If he defeats Capriles, it would leave the opposition in disarray and possibly spark in-fighting over who would be its next presidential candidate.
Two other opposition governors, Pablo Pérez and Henri Falcón, are obvious possibilities. But first they too must retain their posts to maintain credibility, and they do not have the national recognition Capriles achieved during his unsuccessful run for the presidency in October.
Despite losing, he won the opposition's largest share – 6.5 million votes or 45% – against Chávez, and impressed Venezuelans with his energetic style, visits to the remotest corners of the country and attention to day-to-day issues.
"In the unlikely event that Capriles loses, he would probably have no chance of running for the presidency again," political risk consultancy Eurasia Group said.
The mid-December timing of the vote could count against the opposition, many of whose middle-class supporters often take advantage of school holidays to travel. – Reuters