CARACAS (AFP) - Hundreds of thousands of supporters on Sunday crammed Caracas' streets in what opposition presidential hopeful Henrique Capriles, trailing in the polls, called a fast-changing tide.

"Today, we are winning this contest," Mr Capriles, the 40-year-old governor of Miranda state, told masses of faithful, despite polls showing him as many as 20 points behind acting President Nicolas Maduro.

Mr Maduro, 50, is a burly former bus driver and ex vice president who was the anointed successor of late president Hugo Chavez before his death from cancer last month.

Opposition leaders say Mr Maduro has used sympathy for Mr Chavez and the late president's state political machinery to bolster his campaign. But Mr Capriles, a telegenic distance runner whose female fans have endearingly nicknamed "Skinny," was not ready to give up based on polls.

And in fact, his mass support on the capital's streets had him professing confidence that victory - in this country sitting atop the world's largest proven oil reserves - was within reach.

"Just three short weeks ago, they were saying that this was impossible," Mr Capriles said, urging supporters: "Give me your vote of confidence, because I want for this country - which wants change - to be able to achieve it." Mr Capriles, in a wine-coloured shirt the colour of the national football squad's, spoke after masses of his backers thronged the rally from eight separate points around the capital.

He took aim at the Venezuelan government's close relationship with the Communist Cuban government - resented by many here for the vast resources, billions of dollars a year, bestowed on Cuba, and fired.

"You can go ahead and win elections in Havana. I am going to win the elections here in Venezuela," Mr Capriles said jabbing at Mr Maduro.

Reaching out to supporters of the late president Chavez, Mr Capriles also urged them to cross over to his side.

"Vote for me," he said. "Nicolas (Maduro) is not Chavez.

"I am not the opposition," Mr Capriles insisted. "I am the solution." Construction worker William Pereira, 33, said his vote would go to Mr Capriles.

"We have hope. We need a better Venezuela, and that's why we are out here fighting for it," he said along a major avenue with his wife and daughters.

"Maduro is not a strong guy. He thinks he is funny like Chavez, but he is so far from it," added Mr Pereira.

Pro-government supporters gathered on balconies to "challenge" the Capriles rally - particularly in government funded subsidised housing. But the number of Capriles supporters spoke loudly for now.

"The main reason I am here is the public safety crisis. Yesterday my uncle had his car robbed from him - at gunpoint. This cannot go on like this," said accountant Richard Nunes, 28.

"It may be really difficult to pull off a win. But we have to get out and try or we are leaving the whole thing in his hands," Mr Nunes said of Mr Maduro.

"Chavez did good things in terms of investing in the neediest. But he also left the country divided by a political party. And this has got to change," Mr Nunes stressed.

The presidential vote to replace Mr Chavez will be held on April 14.

On Thursday, Mr Maduro also accused the opposition of plotting to sabotage the national power grid to cause a blackout ahead of the election.

He repeated the claim on Saturday, adding that he was aware that one of the leaders of Mr Capriles' Justice First party had met with an employee of the US Embassy in Caracas to discuss plans for "a general blackout" in the state of Bolivar, where most of Venezuela's electrical power is generated.