(CNN) -- A third oil holding tank has gone up in flames at the Amuay oil refinery in northwestern Venezuela, Oil and Mining Minister Rafael Ramirez said Monday.
The death toll has risen to 48, Stella Lugo, governor of the state of Falcon said Monday, two days after an initial explosion there.
"We have been serious, transparent and honest with the (death) figures," she added.
On Sunday, President Hugo Chavez arrived at the refinery to survey the damage.
Speaking to reporters, he said it was too early to speculate what could have caused the blast, which injured more than 80 people.
"There was a leak. The gas formed a cloud and it exploded. We must investigate why," Chavez said.
The president declared three days of mourning.
The early Saturday blast damaged refinery infrastructure and ripped through nearby houses.
Among the dead were 18 members of the national guard and 15 civilians, according to Vice President Elias Jaua, state-run VTV reported.
In total, 209 homes and 11 businesses were damaged, Jaua said.
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.
The organization said 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.
The South American country ships a large percentage of its exports to the United States.
CNN's Marilia Brocchetto contributed to this report.