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
F1's governing body was paid $5 million after it signed a contract with the sport which favours the top teams, ITV News has discovered.
When the Queen arrives for the State Opening of Parliament in June she won't be wearing her crown, dress in robes or arrive in a carriage.
A little more sunshine in store