Almost 7.2 million Venezuelans-lower than the projected 10.5 million out of 19 million possible voters-cast ballots in the symbolic election against Maduro, university guarantors said with 95 percent of votes counted.
"If they're forcing us, it isn't democracy", Madriz said. "What we're trying to accomplish is try to get Venezuela freedom, the same freedom we have here", activist Rangel Melendez said.
Late Sunday Foreign Minister Samuel Moncada said on Twitter that he was declaring former Mexican President Vicente Fox persona non grata and banning him from the country for conspiring to promote violence and foreign intervention.
Xiomara Escot, 61, was killed when a pro-government armed group opened fire at the El Carmen Church polling station in Catia, an impoverished neighbourhood in Venezuela's capital, Caracas.
The proposed constitution is deeply unpopular as it would effectively give Maduro the power to dissolve all government bodies, including the opposition-packed National Assembly.
Through Twitter, the communications office of the bishops' conference shared many pictures of bishops taking part in the referendum, once again taking a clear stance "always on the side of the rights of the people", as Bishop Jose Luis Azuaje Ayala told Crux last May.More news: Honda to recall 2.1 million Accords worldwide after engine fire reports
Isabel Santander, a 67-year-old retired auditor, said she was voting against the constitutional assembly as a protest against the country's economic collapse.
Mr Maduro and military dominate most state institutions, but the Opposition controls Congress and holds three of 23 governorships. The country's chief prosecutor has recently broken with the ruling party. Local media reported that government-backed militias had taken aim at opposition protesters, forcing many to seek refuge as the gun shots rained down.
Just two weeks before an election to decide the delegates who will rewrite Venezuela's national constitution, opposition activists held a symbolic vote of their own on Sunday.
Though polls show the opposition has majority support and his foes repeatedly call for a free and fair election as their top demand, Maduro insists they are USA pawns intent on sabotaging the economy and bringing him down through violence.
Results showed 98.5 per cent of respondents voted in favour of the armed forces protecting the constitution following the decisions of the opposition-controlled National Assembly, which was declared in contempt by the Supreme Court a year ago, stripping it of its powers. Venezuelan authorities have refused to greenlight the vote that has been presented as an act of civil disobedience and supporters of Maduro are boycotting it. Protests against Maduro since April 1 have brought thousands to the streets demanding elections, but has also left 95 people dead, according to an official toll. The petroleum-rich nation has been hit hard by falling world oil prices.