Julio Borges (centre), leader of the opposition-controlled parliament, speaks following the vote. Pic/AFP
Julio Borges (centre), leader of the opposition-controlled parliament, speaks following the vote. Pic/AFP

More than 7 million Venezuelans voted in Sunday's unofficial referendum held by the opposition to heap pressure on President Nicolas Maduro and repudiate his plan to rewrite the OPEC nation's constitution, monitors said.

The symbolic plebiscite was aimed at denting Maduro's legitimacy further amid a crippling economic crisis that has left millions struggling to eat and months of anti-government unrest that has killed nearly 100 people.

Opposition leaders hailed it as a success, while also mourning the death of one woman killed by gunmen in Caracas during the voting.

Maduro, 54, dismissed Sunday's poll as unconstitutional and is campaigning instead for a July 30 vote to create a legislative superbody that would have the power to rewrite the constitution and dissolve state institutions.

The elections council, which the opposition calls a pawn of Maduro, simultaneously held a test-run on Sunday for the July 30 vote to create the constitutional assembly.

Voters were asked three questions at Sunday's event and an overwhelming 98 per cent chose to reject the proposed new assembly, urge the military to defend the existing constitution, and support elections before Maduro's term ends in early 2019, according to academics monitoring the vote for the opposition.

Sunday's participation by nearly 7.2 million Venezuelan voters, compared with 7.7 million opposition votes in the 2015 legislative elections, which they won by a landslide, and the 7.3 million votes for the opposition in a 2013 presidential poll narrowly won by Maduro.