Relatives of Spain train derailment victims mourn loved ones while demanding answers

Prime Minister Pedro Sanchez and Transport Minister Oscar Puente did not attend the service

Relatives of the 45 people killed in Spain's devastating rail disaster have vowed to uncover the truth behind the collision, making their solemn promise at a funeral mass attended by survivors still bearing visible injuries.

"Only the truth will help us heal this wound. We will know the truth, we will fight so that there will never be another train," declared Liliana Saenz, who lost her mother in the tragedy, during the service held in the southern city of Huelva. King Felipe VI and Queen Letizia were present, offering their condolences.

Spain continues to grapple with the aftermath of the January 18 incident near the village of Adamuz, southern Spain, which resulted in one of the highest death tolls from a train crash in European history.

The government has faced intense scrutiny regarding its investment in the maintenance of Spain's acclaimed railway system, particularly following this crash and other incidents that same week, including the death of a train driver in Catalonia.

Notably, Prime Minister Pedro Sanchez and Transport Minister Oscar Puente did not attend the service.

Emergency crews respond after a commuter train derailed when a retaining wall collapsed onto the tracks in Gelida, near Barcelona, Spain (AP)

Authorities have indicated that a fracture in the rail appears to have occurred before one of the trains, en route to Madrid from Malaga, derailed.

It was then struck by a second, Huelva-bound train travelling in the opposite direction, just 20 seconds later. Transport Minister Puente suggested the gap between events could have been as brief as nine seconds.

Addressing a congregation of hundreds of relatives and some survivors, Ms Saenz, flanked by her brother, articulated the profound grief: "We are the 45 families who would trade all the gold in this world, which is now worthless, for the chance to move the hands of the clock forward just 20 seconds."