More than 500 male students and staff were to give DNA samples in an unprecedented operation launched Monday to uncover who raped a 16-year-old girl in the toilets of a French school.

The operation, a first for a French school, has raised concerns over rights violations after prosecutors said anyone refusing to submit a sample would be considered a potential suspect.

The collection of samples began as students arrived for morning classes at the Fenelon-Notre Dame high school, a private Catholic school in the southwestern Atlantic port city of La Rochelle.

It was expected to take until Wednesday for the samples to be collected from 475 students, 31 teachers and 21 other staff on site at the time of the rape.

The girl was raped in a toilet at the school on September 30. The lights in the toilet had been turned off and the girl has not been able to identify her attacker.

A trace of male DNA taken from her clothing will be compared with the samples taken this week.

Individual consent will need to be given for the sample to be taken, as well as parental consent in the case of minors.

The samples will be drawn using a swab under the tongue and the results of the tests are due in several months.

Authorities said samples that do not match the DNA found on the victim will be destroyed.

"We must have the consent of both the parents and the minor," said Isabelle Pagenelle, the prosecutor of La Rochelle, "but those who say no will become potential suspects who could be taken into custody."

Prosecutors said they had decided to go ahead with the mass DNA tests after several months of investigation proved fruitless.

But some have condemned the move as a violation of civil rights.

"Refusing to give a DNA sample when not in custody is a right," prominent defence lawyer Joseph Cohen-Sabban told newspaper Le Figaro.

"It's ludicrous! They want to decide on taking someone into custody based on that person exercising their rights," he said. "Then, once in custody, it's against the law to refuse to give a DNA sample... This is a truly unacceptable abuse of process."

Many of the students said they were willing to give samples in the hopes of tracking down the rapist.

"Everyone is participating without too much trouble because we stand with the girl that was raped and want to find whoever was responsible," said 17-year-old student Lucas.

Concerned about their security, some students asked why authorities waited to move ahead with the tests.

"I don't know why it took so long, it's not normal. It's been seven months that this rapist may be in the school," said 16-year-old Margaux.