CARACAS - Presidential candidates Nicolas Maduro and Henrique Capriles have begun Venezuela's election race with scathing personal attacks even as mourners still file past Hugo Chavez's coffin.

Maduro, who was sworn in as acting president after Chavez died of cancer last week, is seen as favorite to win the April 14 election, bolstered by an oil-financed state apparatus and a wave of public sympathy over Chavez's death.

Venezuela's acting President Nicolas Maduro talks to supporters after he registered as a candidate for president in the April 14 election outside the national election board in Caracas March 11, 2013. [Photo/Agencies]

"I am not Chavez, but I am his son," Maduro told thousands of cheering, red-clad supporters as he formally presented his candidacy to the election board on Monday.

"I am you, a worker. You and I are Chavez, workers and soldiers of the fatherland," the former bus driver and union activist added after the crowd's emotions were whipped up by recordings of Chavez singing the national anthem.

Thumbing his nose at detractors who scoff at his qualifications, Maduro arrived driving a white bus, waving to supporters. His rally congested downtown, and Capriles sent aides to present his papers rather than going personally.

Chavez made clear before his fourth and last cancer operation in December that he wanted Maduro, his vice-president and former foreign minister, to be his Socialist Party's candidate to succeed him if he died.

Maduro has vowed to continue the radical policies of Chavez's 14-year rule in the South American OPEC nation, including the popular use of vast oil revenues for social programs. But Capriles is promising a tough fight.

"Nicolas, it is you who are the problem... you are the voice of lies," Capriles told reporters on Monday, accusing him of minimizing Chavez's medical condition while he prepared his candidacy.

"Death should never be used, particularly not for election campaign ends," added Capriles, who would struggle to govern if elected because the national assembly, courts and other major institutions are dominated by Chavez supporters.

At stake in the election is not only the future of Chavez's leftist "revolution", but the continuation of Venezuelan oil subsidies and other aid crucial to the economies of left-wing allies around Latin America, from Cuba to Bolivia.

Venezuela boasts the world's largest oil reserves.

Government officials said Capriles was playing with fire, offending Chavez's family and risking legal action by criticizing the handling of his illness and death.

"You can see the disgusting face of the fascist that he is," a visibly furious Maduro said, alleging that the opposition was hoping to stir up violence.