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.
Ms. Lugo, governor of Falcon state, said some 48 people had been injured in the blast 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.