The driver of a Spanish train that derailed near Santiago de Compostela has reportedly told judges he was speeding because of "a lapse of concentration" in the moments before the crash that killed 79 people.

Francisco Jose Garzon Amo was released from custody after appearing handcuffed before the regional High Court, as he faces multiple counts of reckless homicide.

Spanish newspaper El Mundo claims that, at the closed hearing, Garzon told Judge Luis Alaez he was travelling at about 190kph when the train came off the tracks on a bend a few kilometres from Santiago.

Garzon said he had got distracted and wasn't really sure about the train's position as it entered a curved stretch near the end of a six-hour journey from Madrid to Ferrol.

When Garzon realised he was travelling far faster than the section's 80kph speed limit he tried to slow down, but it was too late, El Mundo reported.

Gonzalo Ferre, president of Spain's rail network administrator ADIF, said Garzon received a speed warning "four kilometres before the accident happened".

Garzon, a 52-year old from La Coruña in north-west Spain, also reportedly told one rescuer he had been unable to brake.

"He said he had to brake to 80 and couldn't, that he was going fast," local resident Evaristo Iglesias, who rushed to the scene to help injured people out the smashed carriages, told Antena 3.

"He kept saying 'I want to die! I want to die! I don't want to see this!".

Garzon has not been formally charged but has been ordered to appear before a court once a week pending further investigations, the High Court said. He has also his train driving licence suspended and his passport confiscated.

Prime Minister Mariano Rajoy and members of the Spanish royal family are to attend a Mass in homage to the victims of the crash in Santiago.