President Nicolas Maduro on Tuesday blamed Venezuela's right-wing opposition for what he dubbed "sabotage" that prompted blackouts which plunged much of the country into chaos.
"At this hour, all signs indicate that the extreme right has implemented its plan to carry out an Electrical Coup against the nation," leftist Maduro said on Twitter.
"Clearly, behind all this is the hand of those who want to weaken our nation. Onward on the road to work and prosperity. Unity and Progress!" the president tweeted.
By being "alert and active, we will defeat them," Maduro said noting that he had activated troops to step up patrols until power could be restored in the South American OPEC member state.
Oil Minister Rafael Ramirez said the key industry was operating normally and that there were no issues with domestic supply. Venezuela sits atop the world's largest oil reserves.
The blackout struck at peak hours in Caracas, around 12:30 pm local time (1700 GMT), and also affected cities in Lara, Zulia, Tachira, Merida, Flacon, Portuguesa, Cojedes, Yaracuy,
Carabobo, Aragua, Trujillo and part of metro Caracas, according to Electrical Development deputy minister Franco Silva.
Authorities said two power lines had gone down in the country's center-west. It was not immediately clear how Maduro thought his opponents had knocked out power.
The government itself -- then under Hugo Chavez -- had already declared an emergency in the power sector back in 2011 amid huge investment and infrastructure issues.
The Caracas subway service was disrupted by the power failure while outages also knocked out traffic lights, causing transport chaos. Thousands were forced to walk to their homes.
"What a massive mess! I was on the metro and they brought us all out through the emergency exits. I have no idea how I am going to get home," said Zulema Soto, a Caracas resident.
Two hours into the blackout, power was being gradually restored in some areas, Electricity Minister Jesse Chacon said.
Interior Minister Miguel Rodriguez Torres said that there had been no significant criminal events linked to the outages. Street crime and violent offenses are rampant in Venezuela.
The government last week said it had derailed a plot to kill Maduro, arresting two hitmen it said wanted to assassinate the leftist leader on orders from a Colombian conservative ex-president.
The government made frequent allegations of assassination plots against the late leftist President Chavez and has continued to do so under Maduro, his handpicked successor.
Official results gave Maduro, 50, a razor-thin margin of just 1.5 percent over Henrique Capriles, 41, in the April 14 election. Capriles disputes the tight presidential vote results.
"Today's blackout shows how terribly incapable this government is! And then they wheel out another fairy tale to try to hide their failings," Capriles tweeted.