Venezuelan state governor Henrique Capriles looked set to win an opposition primary on Sunday, setting up a battle with President Hugo Chavez in October in South America's top oil exporter.

By mid-evening official results had not yet been announced, but a senior Capriles ally told Reuters he had won, and the governor's camp set up a stage at their Caracas headquarters in apparent preparation for victory celebrations.

Several aides to Pablo Perez, Capriles' biggest competition, also told Reuters their candidate had lost the Democratic Unity coalition election.

Turnout appeared to be around the 2 million mark. The opposition wanted to have a strong turnout ahead of their campaign to end 13 years of Chavez's socialist revolution.

The reaction of losers in Sunday's opposition primary will show if the coalition is ready to rally behind the winner and mount a dynamic campaign that could chip away at Chavez's popularity ahead of the October 7 presidential election.

Miranda state governor Capriles, 39, has led polls for months ahead of Zulia governor Perez, 42, and three other candidates in the primary race.

I aim to be a president who talks much less, who doesn't invade Venezuelans' personal lives so much, Capriles said this week in a pointed reference to Chavez's longwinded speeches, which local media are often obliged to run live.

Capriles hails Brazil's market-friendly but socially conscious policy model as his inspiration and has said he would take a no shocks approach to dismantling Chavez's statist economic policies, such as currency controls.

He might move faster to end controversial friendships with anti-U.S. figures like the leaders of Iran, Cuba and Belarus.

Perez, the governor of Zulia state, had projected himself as the candidate of the poor.

Voting was smooth with long, orderly queues around pro-opposition neighbourhoods of the capital Caracas where walls were plastered with the candidates' posters. Young activists rode motorbikes exhorting voters to head to the polls.

Chavez strongholds were largely devoid of opposition propaganda, however, and state TV gleefully broadcast images of some semi-deserted polling centres with just one or two voters.

(Additional reporting by Girish Gupta, Deisy Buitrago, Editing by Andrew Cawthorne and Brian Ellsworth and Stacey Joyce)