A freight train slammed into a crowded passenger bus at a grade crossing at about 5:00 p.m. Friday in northeastern Mexico. At least 20 people are dead and 31 injured according to the state’s emergency-management office. Rescue crews worked through the night trying to rescue victims. The accident occurred in the town of Anahuac, Nuevo Leon.

The bus was attempting to cross railroad tracks. Images from local media show that the bus was split in half from the force of the train. Usually transporting about 40 people, the bus was travelling with 51 passengers as it went from Nuevo Laredo to Nueva Rosita.

Kansas City Southern de Mexico, the train’s operator issued a statement confirming that there had been a “lamentable accident.” They did not give a cause for the crash. Officials are investigating whether the bus might have been trying to beat the train to the crossing. Four children are among the deceased. According to Jorge Ovidio, Nuevo Leon Civil Protection director, the injured have been taken to the Nuevo Laredo general hospital in Tamaulipas. The driver is in custody.

The accident is the deadliest to occur in Nuevo Leon since a bus-train collision nearly six years ago that killed 18 people.

Authorities in Coauila, Tamaulipas and Nuevo Leon are coordinating on a strategy to assist that families of the victims.