Emergency services workers worked through the night in Mexico City, to search for people trapped in rubble after an explosion hit the headquarters of state-owned oil company Pemex.
Mexican president Enrique Pena Nieto vowed to "work exhaustively to investigate exactly what took place, and if there are people responsible, to apply the force of the law on them."
The death toll rose to 25, and over 100 were thought to be injured.
Shortly after midnight local time, the company said that at least 46 people were still being treated in hospital.
Pemex said the blast would not affect operations.
The state-owned oil provider has been hit by several other safety incidents in recent years.
More top news
Tens of thousands of people paid their respects at a full state funeral for Romania's King who was deposed by Communists in 1947.
Remaining cold for most this weekend with the risk of ice overnight
Last-minute Christmas shoppers have also been warned to watch out for icy pavements as the cold snap continues.