The death toll from the explosion at the headquarters of Mexico’s state-owned oil company has risen to 32.
More than 120 people were injured during Thursday’s blast at the firm Pemex in Mexico City.
The blast caused significant damage to several floors of an administrative building next to the iconic 51 storey Pemex tower.
Several theories have surfaced as to the cause of the tragedy ranging from an electrical fire to an attack.
The company’s director Emilo Lozoya promised a thorough investigation.
“We are working with the best teams from Mexico and abroad to determine what were the root causes (of the explosion). We are not going to speculate or get ahead of ourselves. We’d like to act with the utmost responsibility when it comes to that, thank you very much,” he said.
Mexico’s new president Enrique Peña Nieto visited some of the 52 survivors who remain hospitalised.
Rescue workers continue to sift through the debris for survivors.
A debate over the future of Pemex has raged for some time. Opposition politicians fear plans are under way to part-privatised it.
The world’s number four oil producer is the biggest contributor to Mexico’s economy but has been plagued by falling production and a poor safety record.