Thousands of children fell victim to violence and abuse in Catholic boarding schools in Switzerland up until the 1970s, according to a recent study decrying "sadistic" practices resembling "torture".

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"There was always this incredible fear, fear, fear, fear," recalled a former student of a Catholic boarding school in the German-speaking central Swiss canton of Lucerne.

The former student, whose name was not given, was one of around 50 former boarders at 15 different boarding schools in Lucerne between 1930 and 1970 who in chilling detail testified to their experiences in a report ordered by the canton.

"These interviews were very important for the people in question, because finally their testimony was being taken seriously," said Markus Furrer, the lead author of the report and a professor at the PHZ Lucerne University of Teacher Education.

"Many boarding school children long felt guilty over the experiences they had. Some managed to move on, others failed and some committed suicide," said Furrer, who along with two colleagues had spent a year and a half delving into the murky past of these establishments.

Some cases of violence and sexual abuse were already known, he told AFP, but "we were not expecting it to be this large-scale."

When a child was too noisy or wet the bed, the nuns running the schools used cruel punishments like "pushing small children's heads under water," Furrer said, comparing the practice to "waterboarding", a controversial interrogation technique broadly considered to equate to torture.

The report of around 100 pages, seen by AFP, details the abuses, hardships and humiliations suffered by the Swiss boarding school students, many of whom had been taken from their poor families and placed there by authorities.

Going without food was commonplace, one of the former boarders recalled.

"I cannot remember anyone who wasn't hungry. Basically everyone was hungry," he said.

Children who tried to have a sip of water in between meals were also harshly dealt with, according to the report.

"If someone bent over a faucet to drink, his head would be pushed down so his face hit the faucet," another former student testified.

"The degree of punishment and abuse clearly went well beyond what was admitted to at the time," according to the study, which points out that some teachers showed "sadistic" tendencies and used practices "close to torture," including punching or kicking children in the face.

The teenage students -- both girls and boys -- meanwhile often fell victim to sexual violence from clergy, also of both sexes.

If anyone threatened to talk, the nuns warned them they would face "the wrath of God," according to the report.

"No one believed you, especially when (the accused) was a young priest," one of the victims recalled.

According to the report's authors, more than half of the former students who testified had been subjected to sexual violence.

In March last year, the canton of Lucerne apologized for the abuse already known of at the time.

The Catholic Church meanwhile apologized in 2008 and has also ordered a study into the abuse, which is set to be published next year.

"Punishment was at the time very common in religious circles," said Valentin Beck, another of the Lucerne report authors, pointing out that religious teachers tended to think they were "doing God's work."

The statute of limitation for the crimes committed up until the end of the 1960s has passed, the perpetrators are mostly all dead, and the victims, for their part, have no right to compensation.