Heavy machinery is being used to assist in the recovery following a two-train crash in southern Spain which killed at least 41 people.
Rescuers worked through a second night as more bodies are feared to be trapped in the wreckage.
More than 120 people were injured when carriages on a Madrid-bound train derailed and crossed over to the opposite tracks, hitting an oncoming train in Adamuz on Sunday evening.
A faulty or damaged weld on a rail is being investigated as a factor in the crash, Spanish media report.
Prime Minister Pedro Sanchez has cancelled his planned trip to the World Economic Forum in Davos, pledging to get to the bottom of Spain's worst train disaster in more than a decade.
Spain's King Felipe and Queen Letizia will visit the site later on Tuesday. Three days of national mourning have been announced.
Transport Minister Óscar Puente said the death toll is not yet final. Officials are working to identify the dead.
Puente said the investigation could take at least a month, describing the incident as extremely strange. Current investigations are focusing on a reported 30cm gap in one of the rails.
Ignacio Barron, head of Spain's Commission of Investigation of Rail Accidents (CIAF), stated that the interaction between the track and the vehicle is being scrutinized. Meanwhile, reports suggest the condition of the rail line had been a concern raised by train drivers earlier this year.
Four hundred passengers and staff were on board the two trains. Emergency services treated 122 people, with 41, including children, still in hospitals, of which 12 are in intensive care.
As the investigation continues, the focus remains on what caused this tragic event, which has revealed the vulnerabilities in rail transport safety.
