Spain's transport ministry said it suspected that the communication cables had been cut in a "suspected act of sabotage".
Fibre optic communication cables had been cut around 7am and occured between Vilafranca del Penedés y Gelida, a spokesman from the ministry said during a televised press conference.
As fibre optic cables have no value on the black market it was either a mistake by thieves looking to steal copper cables or a deliberate act of vandalism, according to sources said cited on Vozpopuli website.
Renfe reported that engineers had fixed the problem by 10:45 and that services were expected to return to normal.
It estimated that around 9,500 passengers had been caught up in delays after the entire network of high speed trains in Catalonia had been paralyzed for several hours after robbers stole fibre optic communication cable overnight.
INFO 10:45 Restablecidas las comunicaciones, se reanuda el servicio LAV Barcelona Figueres. Se irá recuperando paulatinamente la normalidad— Adif (@Adif_es) October 8, 2015
The transport was company was left scrambling on Thursday morning to put on replacement bus services to take passenegers to alternative routes.
High speed trains between Barcelona and Madrid were affected as were those trains heading north from Barcelona to the French border.
Pasajeros en Tarragona. Hasta aquí llega el AVE. Luego autobuses. Qué no han aparecido aún. pic.twitter.com/J2hx6PQmT6— Jaime Rodríguez (@JaimeRodrigC) October 8, 2015
Renfe explained that trains had to be cancelled after fibre optic cables were stolen overnight breaking the communication network.
High speed trains between Tarragona and Barcelona were unable to operate and a replacement bus service was in place, the company said.
NFO: Per robatoria de cable, el trajecte entre Camp de Tarragona i Barcelona es realitzarà en autobús. Peguem disculpin les molèsties— Renfe (@Renfe) October 8, 2015