You could see pieces of the wall falling to the ground , '' said Joaquin Borrell Valenzuela , an attorney for the Pemex comptroller 's office , who was in a courtyard outside the building at the time of the blast . At least four people were killed in last night 's explosion . Two people remain missing . The blast happened at the Mexico City headquarters of Pemex , the state - run oil giant . Operations are under way .
At least four people were killed in last night 's explosion . Two people remain missing . The blast happened at the Mexico City headquarters of Pemex , the state - run oil giant . Operations are under way .