At least one person has been shot dead while waiting to vote in an unofficial, opposition-organised referendum in Venezuela.
Opposition activists celebrate outside polling stations after taking part in the opposition-organized vote. Photo: AFP
Men on motorbikes opened fire in the poor neighborhood of Catia in Caracas, where thousands were participating in the event.
They killed one woman and wounded at least three others.
Venezuela is in crisis, with more than 100 people killed in political clashes since April.
The opposition Democratic Unity coalition said the attackers were part of a pro-government "paramilitary" gang.
Video from the scene showed people rushing away from the gunshots. Many fled to a church.
The crowds were gathered to vote in an unofficial poll being held over concerns an official referendum set for 30 July - on whether to accept a new assembly - could herald a dictatorship.
That referendum could grant the assembly power to rewrite the constitution and to dissolve state institutions.
As well as voting on the assembly, people were being asked in the unofficial poll whether they wanted fresh elections before Socialist President Nicolas Maduro's term ends in 2018 and whether they wanted the armed forces to defend the current constitution.
The vote was being held in improvised polling stations at theatres, sports grounds and roundabouts within Venezuela and in more than 100 countries around the world.
Opposition leader Henrique Capriles said in the afternoon that one million Venezuelans abroad had voted.
Venezuelans in Colombia take part in the symbolic plebiscite. Photo: AFP
While it is only symbolic, BBC South America correspondent Katy Watson said the opposition hoped that a high turnout would heap pressure on the government.
Opposition spokesman Carlos Ocariz said of the shooting: "We lament this very much, with great pain.
"But it is just one of 2030 voting centres."
President Nicolas Maduro described Sunday's vote as "meaningless".
A former bus driver and union leader, he denounced the plebiscite as illegal.
"They have convened an internal consultation with the opposition parties, with their own mechanisms, without electoral rulebooks, without prior verification, without further verification. As if they are autonomous and decide on their own," he said.
Volunteers count the ballots during an opposition-organized vote to measure public support for Venezuelan President Nicolas Maduro's plan to rewrite the constitution. Photo: AFP
Catia, where the shooting happened, is a poorer part of the Venezuelan capital where support for the socialist government, headed first by Hugo Chavez and since his death by Mr Maduro, has historically been high.
Mr Maduro, 54, argues the constituent assembly is the only way to help Venezuela out of its economic and political crisis.
He has said that a new constitution would "neutralise" the opposition and defeat "coup-plotters" and thereby promote peace in Venezuela.
Opposition leaders fear that the process of setting up a new constituent assembly and rewriting the constitution would almost certainly delay this year's regional elections and next year's presidential election.
They also fear that the constituent assembly would further weaken the National Assembly, Venezuela's opposition-controlled legislative body.
The opposition promised results on the poll by Sunday evening.
- BBC / Reuters