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
Rain spreads further east through the day.
Renting vehicles is set to be made harder as hiring details offer a new lead in the hunt for the fugitive Barcelona attacks suspect.
Pubs and attractions in Cromer shut early last night after police warned of an outbreak of 'low level disorder'