More than 500 passengers were on board the trains when the incident occurred in the province of Toledo, south of Madrid.
According to the Minister of Transport, the controller ordered all trains stopped in the area to resume running at normal speed, but one of the drivers corrected him by telling him that they had to drive"on sight", which implies traveling at a maximum speed of 40 km/h.
A passenger on one of the trains told local media there was a violent impact about 40 minutes into the journey.
Eighty people were treated for their injuries, authorities said, with 50 reported in serious condition and 15 others in critical condition.
“In the event of a system failure, the control center takes over,” he said, adding that it was the control center which decided to re-authorize the movement of trains, without any speed restriction. “The decision to resume circulation without having resolved the incident rests with the control center,” declared the minister.
“The decision to resume traffic without having resolved the incident rests with the control center.