About 19.5 million people are eligible to elect lawmakers to the 167-seat National Assembly during Sunday's ballot, which is widely seen as a de-facto referendum on the economic leadership of President Nicolas Maduro.

"They say they're winning in the polls - it's the same story of the last 17 years," said Maduro, of the ruling United Socialist Party of Venezuela (PSUV), at one pre-election event. Maduro had taken over as president in 2013, following the death of Hugo Chavez.

"Let them win in the polls; we will win in the streets," he added.

A nationwide survey by pollsters Datanalisis in November estimated some 55.6 percent of voters would back opposition candidates, while 36.8 percent would support government ones. However, the polling did not measure each electoral district, which experts say would be a better gauge of public opinion for this type of vote.

Struggling economy

Venezuela has vast oil reserves but is suffering from soaring inflation and poverty. This year's slump in oil revenues, which fund almost all public spending, has worsened the economic situation.

"There is too much insecurity, too much scarcity. All basic goods are hard to come by: diapers, oil, rice," one voter, 33-year-old Carlos Silvera, told the AFP news agency.

Even if the broad coalition of opposition groups, the Democratic Unity Roundtable (MUD), wins the most votes, under Venezuela's electoral system it is unclear how that would translate to seats in the National Assembly and thereby how much power they would have. Maduro's critics have accused him of rigging the voting districts in his favor.

International authorities have also criticized Venezuelan authorities for not letting more foreign observers monitor the polling.

The lead-up to the election has sparked fears of violence in the South American country. An opposition politician, Luis Manuel Diaz, was shot dead while campaigning on November 26. During anti-Maduro protests last year, a total of 43 people were killed and thousands of demonstrators injured. Dozens of opposition politicians have been detained, including protest leader Leopoldo Lopez, who was sentenced to 13 years jail in a case that drew condemnation from human rights groups.

se/sms (AFP, AP, epd)