|An armed member of the opposition blocks a road as Venezuelans go to the polls|
Opposition parties are boycotting the Constituency Assembly election, claiming President Nicolas Maduro will use its result to crush dissenters and tighten his grip on power.
The president cast his ballot in the capital Caracas.
If successful, President Maduro will essentially govern a one-party state, controlling the powerful 545-member body charged with re-writing the Venezuelan constitution.
:: Vote or lose your home: Venezuela's 'illegal' election
The vote marks the peak of four months of protests that have seen 110 people killed in clashes with riot police.
Opposition to President Maduro has steadily grown beyond its roots in the middle classes to include significant support from the slums in Caracas.
"This is illegal," Juan Vieda, a man staffing a barricade in the capital, told Sky News.
|Mr Vieda called the election 'illegal'|
President Maduro is going all out to boost turnout and increase the election's legitimacy .
State employees, who depend on their free housing and food subsidies, have been bombarded with texts and calls telling them to vote or risk losing their lifelines.
Opponents hope a tiny turnout will expose the illegitimacy of the process.
But the government controls the election returns and there will be no independent oversight.
President Maduro insists the new assembly is the only way to haul Venezuela out of its economic and political crisis, but has not explained how a new constitution would do so.
"We have a card to play: a card that will win this game. And that card is the National Constituent Assembly," he said on Friday.