A huge explosion has ripped through the Mexico City headquarters of the state-owned oil giant Pemex, killing 32 people and injuring more than 120.
The mid-afternoon blast shattered the towers lower floors sparking panic as employees fled the building and debris rained down into the streets.
The cause is unknown, but unconfirmed reports suggest a gas boiler exploded.
Rescue teams fear that many workers may well be trapped in the building and the number of casualties is likely to increase.
President Enrique Pena Nieto arrived on the scene and vowed a thorough investigation into the incident, backed by the full force of the law.
Nieto has already said his administration will conduct an overhaul of the company.
Later the president visited the injured in hospital.
The catastrophe is the latest in a number of safety incidents to hit the monopoly.
As recently as last September, 30 people died after an explosion at a Pemex gas facility in New Mexico.