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(CNN) -- An explosion rocked the Amuay oil refinery in northwestern Venezuela, killing 39 people, including a 10-year-old boy, a Venezuelan official said Saturday.
More than 80 people were injured, Vice President Elias Jaua told state-run VTV.
"People are very scared," said Falcon State Gov. Stella Lugo, according to the state-run AVN news agency. "They evacuated the areas that had to be evacuated, but the situation, as the technicians are telling within the refinery, is controlled."
President Hugo Chavez decreed three days of mourning and gave his condolences to families of the victims.
The incident occurred at 1:11 a.m. when "we had a release of gas whose origin we are going to determine," Rafael Ramirez, president of the state-owned petroleum company PDVSA, told VTV. "The gas generated a cloud that then exploded and provoked fires in at least two tanks of the refinery and in the surrounding areas."
He said the explosion damaged the infrastructure of the refinery and nearby houses.
The refinery -- one of the world's largest -- is part of the giant Paraguana complex in Falcon state.
Venezuela, a founding member of the Organization of the Petroleum Exporting Countries, is one of the world's largest oil exporters.
The nation has a refinery capacity of more than 1 million barrels per day, according to OPEC.
Venezuela's oil revenues represent some 94% of the country's export earnings, more than half of federal budget revenues and some 30% of gross domestic product, OPEC says.
The South American country sends a large percentage of its exports to the United States, according to the U.S. Energy Information Administration.
CNN's Pierre Meilhan and Nelson Quinones contributed to this report.