Authorities confirmed on Monday morning that the nationalities of the victims were seven Italians and one German, one Frenchwoman, two Austrians, one Romanian and one woman from Uzbekistan, all aged between 19 and 25.
Emergency services said 19 nationalities were involved in the crash including students in their twenties from the UK, Ireland, Peru, Bulgaria, Poland, Palestine, Japan, Ukraine, the Czech Republic, New Zealand, Hungary, Sweden, Norway and Switzerland.
Photo: EPA/JAUME SELLART
The accident occurred just before 6 a.m. (05:00 GMT) near the small town of Freginals, about 150 kilometres (95 miles) south of Barcelona as the students were returning from the Fallas festival in eastern Valencia known for the burning of giant statues.
The bus driver "hit the railing on the right and swerved to the left so violently that the bus veered onto the other side of the highway," said Jordi Jane, of the Catalan regional interior ministry.
The bus then hit a car coming in the opposite direction, injuring two people inside, he added.
Spain's Interior Minister Jorge Fernandez Diaz, who went to the scene, said it was still not clear why the bus driver hit the railing in the first place, adding however that the accident was likely due to a "human factor".
"It appears an undetermined human error and not a mechanical failure was to blame," he said on a visit to the crash scene on Sunday afternoon. "The driver has tested negative for alcohol and drugs so those factors are ruled out."
The driver, who broke down when questioned by the Catalan police force Los Mossos d'Esquadra, will be questioned by an investigating magistrate at 10am on Monday.
The driver had 17 years experience and no reported accidents.
Identification of the victims is proving difficult because although the students all had assigned coaches and seat numbers on the journey to Valencia, they sat wherever they chose on the return journey.
Jose Roncero Pallares, the mayor of Freginals, said the accidents that had hit that stretch of the motorway over the past years had always taken place in the area where the crash happened.
"I don't know why, the highway looks fine and it's a straight line," he told AFP.
"It rained a lot that night and maybe that played a role."
Catalonia's high court said in a statement that an initial probe revealed "the bus driver tested negative for drugs and alcohol".
The Erasmus Student organization said it was "deeply saddened to inform about the traffic accident suffered by a bus in which exchange students and volunteers from the organisation were travelling.
"Taking into consideration the sensitivity of the issue, Erasmus Student Network Spain would like to request the public for discretion in respect for the families and friends, to whom we send our deepest condolences. In addition, we would like to thank all the volunteers and emergency services for their diligent work in these sad circumstances."
This story was updated to reflect that two Austrians were among the dead.