(updates casualties, adds details)
Thirty-three people died in a powerful explosion at the headquarters of state-owned oil monopoly Petroleos Mexicanos, the Mexican government said Friday.
"The latest information regarding what happened at Pemex Tower is 33 people deceased," Government Secretary Miguel Angel Osorio Chong said on Twitter.
Neither Pemex nor authorities have ventured to speculate on the cause of Thursday's blast inside the 51-story structure, but media outlets said it could have been triggered by an overheating problem in the electrical system.
Details will be forthcoming once experts have completed their inspection of the scene, Mexican President Enrique Peña Nieto said Friday after visiting some of the 121 injured survivors.
"We won't speculate, nor will we get ahead of ourselves. We want to act in an absolutely responsible way," Pemex CEO Emilio Lozoya said at a brief press conference, though he later told a television network that everything indicated the blast was an accident.
Peña Nieto expressed solidarity with the families of the victims and promised them the "full support" of the government.
Numerous shattered windows and structural damage could be observed from outside the Pemex complex, the workplace for some 10,000 people, including around 1,700 in the stricken tower.
"I was on the bottom floor when I felt the explosion. When I saw what was happening I tried to run, but I was thrown by the explosion, I was injured and broke a finger," Jesus Eduardo, a 23-year-old maintenance worker, told Efe.
"First I saw a co-worker who had his legs severed and next to him a lot of people dead," he added. EFE