It was the second massive outage in just over four months on the OPEC nation's electricity grid, which is creaking from outdated infrastructure and low investment.
There were no reports of problems in the country's mainstay oil industry, which is a leading supplier to the United States, the state oil company said.
In some areas, such as the central commercial city of Barquisimeto, electricity was lost for only a few seconds.
And the government moved to assure residents that electricity was being restored quickly in affected areas.
Supply began returning to parts of the capital and would soon start to be restored in other regions, a senior government electricity official, Hipolito Izquierdo, told state television.
Witnesses confirmed some power was being restored to parts of the capital as lights began flickering back on before Caracas's busy rush hour was set to begin. Electricity was slowly returning across the western oil-producing state of Zulia too, witnesses said.
But the capital's underground train system, which hundreds of thousands of commuters planned to use to return home later on September 1, was not operating due to the blackout.
Long lines formed at the main airport outside Caracas as computers failed, preventing passengers from checking in, and flights were delayed. Travelers, sweating without air conditioning, cheered when the lights came back.
The government did not immediately know the cause of the outage that was triggered by a problem in a provincial transmission line, Izquierdo said.
In April, an even larger blackout hit Venezuela and officials failed to restore power for several hours.
That outage caused chaos for commuters who were caught in snarled traffic or forced to walk miles (kilometers) home as underground trains stopped operating and armed troops poured onto the streets to keep order.
After that outage, the government of President Hugo Chavez acknowledged there has been too little investment in the electricity grid over the last few years. It promised massive spending but warned it could take time for the new investment to improve the system.
Last year, the leftist government nationalized the country's largest private electricity company.
Venezuela's oil refineries suffer frequent outages due to power outages, although they generally do not depend on the national grid for their supply.
The April outage caused "some problems" to oil operations, officials acknowledged without elaborating.