Cranes had worked through the night to lift parts of the wreckage of Wednesday's crash while emergency workers removed what appeared to be a body wrapped in a blanket from one of the trains in the central Spanish province of Toledo.
Regional leader Emiliano Garcia-Page said the number of deaths had risen to 69 and that human remains had been found during rescue efforts, which now involved crane operations, particularly on a carriage that remained overturned.
Spain's foreign ministry said 42 foreign citizens from seven countries were involved in the crash, information available so far showed, of whom one was killed and at least seven injured.
Among those killed in Europe's deadliest train accident since a derailment in Santiago de Compostela in 2013 was Fatima Banez, a former labour minister who chaired the social and corporate responsibility arm of Spain's employers' association.
Authorities said 57 of those injured remained in hospital.
People responded swiftly to a call for blood donations after the accident.
In Castilla-La Mancha alone, the region where the collision occurred, more than 2000 people volunteered in the aftermath.
"I want to express my personal and very sincere gratitude to everyone who has stepped up, starting with the all-time record number of donations," Garcia-Page said.
As shocked Spaniards searched for answers on why another crash had occurred, train drivers went ahead with a previously planned strike to press for more investment in railway safety.
"We will continue demanding the necessary measures to make this sector safe again ... It must have all the safety systems required to maintain the quality standards we have always had," Diego Martín of the train drivers' union SEMAF said.
"We cannot tolerate, under any circumstances, this type of incident happening again," he said at Madrid's Atocha railway station.
State-run rail operator Renfe said the strike caused significant disruption to rail services and passengers could change or cancel tickets free of charge and would be notified of affected services.
The Spanish government has declared three days of mourning for those killed in the crash, which Transport Minister Oscar Puente said on Wednesday happened after several trains stopped due to a signal failure.
A Renfe train was then authorised to proceed at normal speed, even though there was a stationary Iryo-operated train ahead, Puente said.
Unions blamed a lack of funding and will to improve safety, saying talks after January's crash were abandoned by the government in April.
Speaking on Wednesday, Puente rejected criticism that the Spanish railway system was unsafe, saying it was "reliable and safe ... with the limits of the material itself and of human action, as is the case with any form of transport".
The government, meanwhile, has said that the decision to authorise the Renfe train to continue its journey was "inexplicable".
As investigations began, a judge in Toledo barred anyone not involved in emergency, security, healthcare or judicial work from the crash site with a 2km exclusion zone in both directions along the Madrid-Seville high-speed rail line.
with AP
