Caracas: Venezuelan President Hugo Chavez flew to Havana for treatment of what is believed to be a malignant lesion in the same part of his body where Cuban doctors removed a cancerous tumour in 2011.

The 57 year-old Chavez, who is seeking re-election in October, vowed to defeat "this new difficulty" just ahead of boarding his flight to Havana, state media reported.

Chavez arrived at the airport in a caravan along with thousands of supporters, and then, flanked by his two daughters, told the crowd and the TV cameras that he will show a strong will for "this new battle" to "defeat the threat" of the illness.

Chavez underwent surgery and four rounds of chemotherapy in Cuba last summer after cancer was detected in his pelvic region. The government has provided few details about the president's health, and in October Chavez announced that he was cancer-free.

But on Tuesday he said that doctors had detected a new "lesion," and late Thursday he warned that it could be malignant.

"Nobody can say right now that it is another malignant tumor... (but) the likelihood of malignancy is greater than the probability that it is not," Chavez said during an event broadcast on state-run television.

Chavez said the operation could take place Monday or Tuesday.

Brazilian President Dilma Rousseff on Friday telephoned Chavez just before he left Caracas to wish him good luck with the surgery, her office said.

Venezuela, one of the world's top oil producers, faces a period of uncertainty as it ramps up for what is likely to be the most closely contested presidential election in years.

Chavez faces a strong challenge in the October 7 presidential election from 39-year-old Henrique Capriles, who was chosen as the sole opposition candidate in a primary earlier this month.

Chavez could still appoint a successor to run in his place, delay the October vote, or soldier on and focus the campaign on his left-wing legacy.

Opposition legislators asked that Chavez delegate powers to Vice President Elias Jaua during his absence, but the pro-government majority in the National Assembly rejected the request.