A nurse aged 61 has been shot dead while waiting to vote in an unofficial, opposition-organised referendum in Venezuela's capital, Caracas.
Men on motorbikes fired at a queue, killing her and wounding three others.
The opposition blamed a "paramilitary" gang. Video from the scene showed people rushing away from the gunshots. Many fled to a church.
Venezuela is in crisis, and more than 100 people have died in political clashes since April.
Opposition spokesman Carlos Ocariz said of the shooting: "We lament this very much, with great pain."
Prosecutors said they would investigate the incident, and the woman was named as Xiomara Soledad Scott.
She died minutes after reaching hospital.
Separately, journalist Luis Olavarrieta was kidnapped, robbed and beaten by a group of people. He managed to escape and images emerged of him receiving medical attention.
An official vote will be held on 30 July on whether to accept a new assembly that would have the power to rewrite the constitution and to dissolve state institutions.
But critics say the new assembly could herald dictatorship.
Opposition politicians organised Sunday's unofficial poll, held in improvised polling stations at theatres, sports grounds and roundabouts within Venezuela and in more than 100 countries around the world.
Voting has now closed.
While the vote was only symbolic, BBC South America correspondent Katy Watson said the opposition hoped that a high turnout would heap pressure on the government.
As well as voting on the assembly, people are being asked whether they want fresh elections before Socialist President Nicolas Maduro's term ends in 2018 and whether they want the armed forces to defend the current constitution.
Queues started to form early and there was a festive atmosphere in most places.
But President Nicolas Maduro described Sunday's vote as "meaningless".
"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.
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 Maduro, has historically been high.
Maduro argues that 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.
What's happening in Venezuela?
- The country is in a deep economic crisis, made worse by the falling price of oil, which accounts for about 95% of its export revenues and was used to finance some of the government's generous social programmes. Forced to make cuts, President Nicolas Maduro has seen his support fall among core backers
- Also, as a result of the crisis, parts of Venezuela face severe shortages of basic supplies such as medicine and food
- The opposition accuses Maduro of not only mismanaging the economy but also eroding the country's democratic institutions
- In March, the Supreme Court decided it would take over the National Assembly. The decision was reversed, but Maduro was accused by opponents of trying to stage a coup. That sparked almost daily protests calling for his resignation
- Meanwhile, Maduro says the opposition is trying to overthrow his government illegally, and blames the country's problems on an "economic war" being waged against him