Stella Lugo said there was no risk of further explosions at the Amuay plant in the north of the country.
Officials earlier said a gas tank had blown up during the night, damaging the plant and nearby buildings.
The Amuay refinery is one of the biggest in the world, producing some 645,000 barrels a day.
Officials have been giving regular updates on the number of dead and injured.
Stella Lugo, governor of Falcon state, earlier said seven had died but later revised the figure to 19.
She also said more than 50 people had been injured and were being treated in local hospitals.
She said there was still a big fire at the plant, but the situation was under control.
Earlier, Energy Minister Rafael Ramirez blamed the explosion on a gas leak.
“It was a significant explosion, there is appreciable damage to infrastructure and houses opposite the refinery,” he said.
Analysts say refineries in Venezuela, South America’s biggest oil producer, have suffered from a long list of problems including power failures and accidents.
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