For the first time in 16 years of "Bolivarian revolution" under late president Hugo Chavez and his successor Nicolas Maduro, polls show their rivals could now win a majority in the National Assembly.
That would strengthen the hand of the opposition even though several of its leaders are in jail, throwing up a challenge to the mustachioed Maduro as he grapples with a serious economic crisis.
"There will be a new political landscape and balance of power," said Luis Vicente Leon, president of the Venezuelan pollster Datanalisis.
"If the opposition wins and is smart, it will negotiate for change. But if opposition radicals take control who just want to get rid of the president, they will lose a golden opportunity" for reform, he added.
The opposition coalition MUD has vowed to rescue the country from the economic management of the "Chavistas."
Maduro has vowed to keep control of the country "no matter how" and dismisses the opposition as stooges of "Yankee imperialism."
"They say they are for change. They are a false change. They are useless. We have built a million homes and they have not built a single one," Maduro told thousands of supporters at his closing campaign rally in Caracas.
"I am ready to do much more to radicalize the revolution of our economy and production," he bellowed, dressed in his trademark tracksuit with the red, yellow and blue Venezuelan national colors.
'Bomb Ready to Explode'
Some fear a repeat of the deadly street clashes that left 43 people dead last year during protests against Maduro.
One opposition leader, former presidential candidate Henrique Capriles, called for peaceful change and warned radicals in the opposition against stirring up fresh unrest.
"Venezuela is a bomb ready to explode," Capriles told AFP.
He and other opposition figures accused the government of being behind violent incidents during campaigning. One opposition leader was shot dead at a rally. Maduro angrily denied any responsibility for violence.
The Latin American nation of 30 million people is in a deep economic crisis due to plunging world oil prices. Families are suffering shortages of basic supplies such as flour and diapers.
It also has the second-highest murder rate in the world after Honduras, according to the United Nations.
"There is too much insecurity, too much scarcity. All basic goods are hard to come by: nappies, oil, rice," said Carlos Silvera, 33, at the closing opposition rally in Caracas on Thursday, in a sea of red, yellow and blue flags.
Venezuela has the biggest petrol reserves in the world but economists forecast its economy will shrink by 10 percent this year. The government says inflation is 85 percent but independent economists say it is more like 200 percent.
Maduro has warned the opposition will take away people's welfare subsidies. He and his supporters vow to continue Chavez's work.
"If it were not for commander Chavez ordinary people would not have access to public education," said Johan Gutierrez, 26, a supporter at Maduro's rally.
"If we lose the National Assembly, the opposition will not approve spending for the great investments and great works of the Bolivarian revolution."
The opposition has not made concrete economic proposals.
It has vowed to try push for an amnesty for political prisoners and possible constitutional measures to drive Maduro from office, if it wins a big enough majority.
But analysts point out Maduro will still be president and say changes to the system of electoral districts could limit the opposition's gains.
"Policy paralysis is expected," wrote Diego Moya-Ocampos, an analyst at financial research group IHS Insight, in a report.
"The opposition will not have a solid majority to push the country's necessary economic reforms and the government does not have the political capital to conduct an economic adjustment program on the scale needed," he added.
"Maduro's ability to complete his term up to 2019 will depend on his government's ability to prevent widespread social unrest and looting, while also maintaining military support."
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