Thirty-two people died and more than 120 were injured in an explosion at the headquarters of Mexico's state-owned oil company, Pemex.
The cause of the basement explosion in an administrative building next to the 51-story Pemex tower in Mexico City remains unknown.
President Enrique Pena Nieto urging people not to speculate.
Reports said three floors of the tower were heavily damaged by an explosion in the basement of an adjacent administrative building.
The blast sent hundreds into the streets and a large plume of smoke over the skyline.
The tower, where several thousand people work, was evacuated.
Police landed four rescue helicopters to remove the dead or injured.
Streets surrounding the building were closed as evacuees wandered around, and rescue crews loaded the injured into ambulances.
Based on reporting by AP and Reuters