Four carriages overturned in the smash late Wednesday, smoke billowing from the wreckage, as bodies were lain out under blankets along the tracks.
The wagons piled into each other and folded up like an accordion. One was ripped apart by the force of the crash, one of its ends pushed up into the air.
Several witnesses spoke of a loud explosion.
The accident happened at 8:42 pm (1842 GMT) Wednesday as the train carrying 218 passengers and four staff was about to enter Santiago de Compostela station in the northwestern region of Galicia.
Rescue workers recovered 73 bodies from the train's wreckage and four more victims died later in hospital, said a spokesman for the Galicia high court, increasing an earlier toll figure.
A total of 143 people were said to have various injuries.
The train had left Madrid and was heading for the town of Ferrol as the Galicia region was preparing celebrations in honor of its patron saint James.
Public television TVE said the train may have derailed because it was speeding at the time of the accident but a spokesman for state railway company Renfe said it was too soon to say what caused the accident.
Earlier, it was suggested the train was travelling at 180 kilometers per hour when the accident happened.
The accident happened on a stretch of high-speed track about four kilometers (2.5 miles) from the main train station in Santiago de Compostela, the destination of the famous El Camino de Santiago pilgrimage which has been followed by Christians since the Middle Ages.
NJF/NJF