The blast occurred after 1 a.m. when a gas leak created a cloud that ignited, Ramirez said. Some nearby houses were damaged by the blast, he said on television.
"That gas generated a cloud that later exploded and has caused fires in at least two tanks of the refinery and surrounding areas," Ramirez said. "The blast wave was of a significant magnitude."
Images in state media showed the flames casting an orange glow against the night sky. One photograph showed an injured man being wheeled away on a stretcher.
"The areas that had to be evacuated were evacuated," Lugo said, according to the state-run Venezuelan News Agency. "The situation is controlled. Of course they're still a fire rising very high, but ... the specialists tell me there is no risk of another explosion."
Ramirez said oil workers will determine what caused the gas leak and were inspecting the damage along with troops. Ramirez said that nine storage tanks were damaged. He said supplies of fuel had been cut off to part of the refinery, and that the fire had been brought under control.
Troops were securing the area at the refinery, Lugo said.
"At this time, the situation is controlled," Jaua said on television, while smoke continued to rise from the refinery. Jaua said earlier on his Twitter account that the military was deployed to the area and that air ambulances were dispatched to ferry the wounded.
Amuay is part of the Paraguana Refinery Complex, which also includes the adjacent Cardon refinery. Together, the two refineries process about 900,000 barrels of crude per day and 200,000 barrels of gasoline.
Venezuela is a major supplier of oil to the U.S. and a member of the Organization of Petroleum Exporting Countries.