The driver of a train that derailed in Spain last week, killing 79 people, was on the phone to a co-worker at the time of the accident, while the train was racing at nearly twice the speed limit.

The Superior Court of Justice of Galicia, which is leading the investigation, issued a statement saying the train's two data-recording black boxes showed that moments before the crash, the train was travelling at 192 kilometres per hour.

Driver Francisco Jose Garzon Amo was also speaking on his work phone to staff members of state railway company Renfe, and appeared to consult a map at the time of the accident.

"Seconds before the accident the brakes were activated. It is estimated that at the time of the derailment the train was travelling at 153kph," the court said.

"Minutes before the train came off the tracks he received a call on his work phone to get indications on the route he had to take to get to Ferrol.

"From the content of the conversation and background noise, it seems that the driver consulted a map or paper document."

Key points: The two data-recording black boxes onboard a train that crashed in Spain last week, killing 79 people, showed the train was travelling at 192kph - nearly twice the speed limit

The two data-recording black boxes onboard a train that crashed in Spain last week, killing 79 people, showed the train was travelling at 192kph - nearly twice the speed limit Train driver Francisco Jose Garzon Amo was also speaking on the phone and appeared to consult a map at the time of the accident

Train driver Francisco Jose Garzon Amo was also speaking on the phone and appeared to consult a map at the time of the accident Garzon Amo was charged with 79 counts of reckless homicide and released under court supervision

The speed limit at the spot where the Madrid to Ferrol train derailed on the outskirts of Santiago de Compostela is 80kph.

The eight-carriage train flew off the tracks on a bend and ploughed into a concrete siding about four kilometres from the town.

A US woman critically injured in the crash died in hospital on Sunday, bringing the toll to 79, including nine foreigners.

It was Spain's deadliest train accident in decades.

Driver admitted lapse of concentration, didn't know where he was

Examining judge Luis Alaez charged Garzon Amo with 79 counts of reckless homicide and released him under court supervision.

The 52-year-old admitted during his court appearance on Sunday that he had had a "lapse" of concentration, according to Spanish media reports.

An official inspects the engine of the train which derailed and crashed killing 79 people. ( Reuters:Eloy Alonso )

Several newspapers said the driver told the judge he had confused the stretch of track he was on at the time of the accident with another part of the route.

"He believed he was on a different section of the track and when he started to slow down it was too late to keep control of the train," newspaper El Pais wrote.

State railway track operator Adif is checking all tracks and security systems in its network in the wake of the accident, a company spokeswoman said.

"This is a precautionary measure. After what happened, the protocol is to review all systems to confirm that everything is working properly," she said.

The train was on a route that uses both high-speed and conventional track.

On the high-speed sections, a sophisticated security system automatically slows down trains that are going too fast.

The accident happened on a conventional section of the track where the older security system in place only automatically stops trains going above 200kph where it is up to the driver to respond to prompts to slow down.

The driver had complained in the past about the security system in place at the spot of the accident did not automatically brake all speeding trains, a spokesman for the Galician branch of the Semaf train drivers union, Rafael Rico, said.

Sorry, this video has expired WARNING: GRAPHIC FOOTAGE. Watch the video footage of the derailment and aftermath

"He himself had said that it was incredible that speed was not controlled at this spot, that you could not go directly from 200kph to 80kph without the supervision of any security system," he told AFP.

Garzon Amo had been with the firm for 30 years, including 13 years as a driver, and had driven trains past the spot where the accident occurred 60 times, the train company Renfe said.

Sixty-six people caught up in the crash were still in hospital, 15 of them critically including one child, regional health authorities said.

Hundreds of mourners attended a memorial mass for the victims in the cathedral in Santiago de Compostela which was broadcast live on Spanish television.

Many aboard the train were Catholic pilgrims heading for Santiago's internationally celebrated annual festival honouring Saint James, a disciple of Jesus whose bones are said to rest in the city's cathedral.

ABC/AFP