"It zigzagged from left to right then turned onto its left side. Then another vehicle ploughed into it," explained a Peruvian student named in La Vanguardia newspaper as Hans.
Most of the 57 students travelling on the bus were sleeping at the time of the crash which occurred just before 6am on Sunday morning, having spent the previous day at Las Fallas festival in Valencia.
Hans, a 20-year-old marketing student on a placement at Barcelona university said that when the bus was lying on its side, it was hit by a vehicle which smashed the windscreen enabling some to escape the wreckage.
Speaking to La Vanguardia on Monday as hundreds gathered at Barcelona University to pay homage to the victims, Hans said he had crawled out of the wreckage through the windscreen, walking away from the disaster with only a bruised face and a broken wrist.
Students gathered at Barcelona on Monday to mourn the victims. Photo Pau Berrena / AFP
"The images and memories of what happened are very painful," he said.
Students who survived the crash have described the sickening moment the coach lurched before overturning.
Bojana Stocjanovska, a student at the University of Bologna who has been studying in Barcelona on the Erasmus programme described how she was jolted awake.
"I was woken by a sudden movement and then we crashed," she told La Informacion from hospital, where she was treated for wounds on her face and arms. "There was no time to think. I was very frightened and in shock."
Meanwhile, one student from the Basque Country told the newspaper: "I am only alive because I was wearing a seatbelt."
British teenage Tallulah Lyons told the BBC that survived the crash and crawled from the wreckage despite having a broken vertabrae.
The 19-year-old Southampton University student from Swindon was taken to hospital in Tarragona with fractured vertebrae.
"I just remember waking up and people were on the floor," she said.
"I was trying to crawl out with friends - and that's when we realised some people were trapped. It took about two hours to get everyone out."
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Thirteen women, - seven Italians, two Austrians and one each from Germany, France, Romania and Uzbekistan - were killed in the crash which occured on the AP7 highway near Freginals, halfway between Valencia and Barcelona in the province of Tarragona.
A further 24 passengers on the bus were still in hospital on Monday, with six described as being in a "serious condition" and one in a "critical condition".
The bus driver is currently being treated in hospital after suffering chest pains and therefore did not have to appear before an investigating magistrate on Monday morning.
Investigators are probing whether the driver, who tested negative for alcohol or drugs, may have fallen asleep at the wheel.