CARACAS (AFP, REUTERS) - A wave of bloodshed swept Venezuela on Sunday (July 30) as troops cracked down on violent protests against elections to choose the members of a powerful assembly that President Nicolas Maduro has tasked with writing a new Constitution.

At least nine people were killed as protesters attacked polling stations and barricaded streets around the country - drawing a bloody response from security forces, who opened fire with live ammunition in some cases.

"This is war!" Caracas resident Conchita Ramirez exclaimed on television as she described troops firing at people and buildings in the capital.

The unrest confirmed fears over the vote for a new "Constituent Assembly" called by Maduro in defiance of months of demonstrations and fierce international criticism.

The socialist president is gambling his four-year rule on the 545-member citizens' body that will be empowered to dissolve the opposition-controlled congress and rewrite the constitution.

Nine people were killed overnight and into Sunday, according to prosecutors, bringing the death toll in four months of violence to some 120 people.

Among those killed was a 39-year-old lawyer in the southeastern town of Ciudad Bolivar who was a candidate for the new assembly. He was shot by assailants in his home late Saturday. Prosecutors said the motive was unknown.

Shootings at protests on Sunday killed a 13-year-old and a 17-year-old in the western state of Tachira. A soldier was also shot dead there.

The death toll also included a 30-year-old regional leader of a youth opposition party in the northeast town of Cumana and two protesters in the western state of Merida.

In eastern Caraca, seven police were wounded when an improvised explosive targeted their motorcycle convoy.

National guard troops used armoured vehicles, rubber bullets and tear gas to disperse protesters blocking roads in the west of the city.

Soldiers also violently moved against protesters in the second city of Maracaibo, in the west, and Puerto Ordaz in the east.

The opposition had called for a boycott and mass demonstrations against the election, which it called a bid by Maduro to install a dictatorship.

"This constituent assembly is being born in a bloodbath. It is born illegitimate," said Nicmer Evans, a prominent socialist turned Maduro critic, alleging widespread irregularities.

Maduro kicked off voting by casting his ballot in a west Caracas polling station.

"I'm the first voter in the country. I ask God for his blessings so the people can freely exercise their democratic right to vote," the president said. He was accompanied by his wife, Cilia Flores, a candidate for the new assembly.

He got a technological snub when he scanned his ID card at the polling station and the screen spit out the words, "This person does not exist or the ID was cancelled." Turnout will be key to determining the legitimacy of the election.

But that will be difficult to ascertain as most voters will be able to vote twice: once by region and once by social or industrial sector.

Voting was extended by an hour, to 7:00 pm, to accommodate what officials described as long lines, despite reports to the contrary.

According to polling firm Datanalisis, more than 70 per cent of Venezuelans opposed the idea of the new assembly - and 80 per cent reject Maduro's leadership.

Maduro decreed a ban on protests during and after the vote, threatening prison terms of up to 10 years.

But protesters flooded the streets in defiance.

"The people are not going to give up the streets until this awful government goes," protester Carlos Zambrano, 54, told AFP in western Caracas.

- 'A sham' - .

Fear of the violence worsening has rippled across the region, and beyond.

The US, the EU and Latin American powers, including Argentina, Brazil, Colombia and Mexico, have condemned the election.

"Maduro's sham election is another step toward dictatorship," tweeted US envoy to the United Nations Nikki Haley.

Britain's junior foreign minister Alan Duncan also described the vote as a "sham," as did many experts.

"The vote means the end of any trace of democratic rule. Maduro's blatant power grab removes any ambiguity about whether Venezuela is a democracy," said Michael Shifter, head of the Inter-American Dialogue research center.

Several foreign airlines, including Air France, Delta, Avianca and Iberia have suspended flights to Venezuela over security concerns.

The US has ordered the families of its diplomats to leave after imposing sanctions on 13 current and former Venezuelan officials.

Maduro, whose term is meant to end in 2019, describes the election as the most important in Venezuelan history.

"I have come to vote to tell the gringos and the opposition that we want peace, not war, and that we support Maduro," said voter Ana Contreras.

Colombia, Panama and Peru - refuges for tens of thousands of Venezuelans fleeing the chaos at home - have said they will not recognise the results of the election.

The US has suggested further sanctions could follow.

US officials told Reuters the Trump administration is considering imposing some US sanctions on Venezuela's vital oil sector in response to Sunday's election.

The measures, which could be announced as early as Monday, are not expected to include a ban on Venezuelan oil shipments to the US - one of the harshest options - but could block sale of lighter US crude that Venezuela mixes with its heavy crude and then exports, the officials told Reuters.