Electrical Energy Minister Jesse Chacon said on state TV that the failure was in the "backbone" that carries electricity from the Bajo Caroni region, where 60 percent of Venezuela's power is generated.
President Nicolas Maduro said Tuesday night that 14 of 23 states lost power for much of the day and blamed "sabotage," which he did not detail. He said service was "progressively restored" with some exceptions, including the oil-producing state of Zulia.
Power that was lost at midday was restored in Caracas by nightfall.
Despite possessing the world's largest proven oil reserves, Venezuela has been plagued in recent years by worsening power outages. They have, however, rarely affected metropolitan Caracas, home to more than one-sixth of the country's 28 million people.
Maduro said the oil industry, the lifeblood of the economy, was not affected by the outage. He blamed "the extreme right-wing," as he has in the past, via Twitter.
In an evening event broadcast on state TV, he claimed the outage was "part of a low-level war" on what his government refers to as "the revolution" begun by the late President Hugo Chavez, Maduro's political mentor. He provided no evidence of any sabotage.
Maduro said he had ordered the military to "protect the entire country."
The capital's subway service was temporarily interrupted, and authorities evacuated riders from several trains.
Opposition politicians say the government, while spending billions on programs for the poor, hasn't invested sufficiently in the electrical grid and generating plants to keep up with growing demand.
Authorities say delays in several initiatives designed to boost electricity output are partly to blame.
Chacon, a longtime close aide to Chavez, was named energy minister after Maduro won election in April by a razor-thin margin. The previous energy minister was a brother of Chavez, Argenis.
Chavez died in March after 14 years in power. Maduro was his longtime foreign minister and later, while Chavez was dying of cancer, his vice president.