French police took DNA samples from hundreds of male pupils and staff on Monday in the hope the mass test could help them find the assailant who raped a 16-year-old girl in the toilets of a school in western France last September.

Two police officers were deployed to take DNA samples from under the tongues of 475 school boys, 31 teachers and 21 staff believed present at the premises of the Catholic secondary level school at the time of the attack.

The victim was attacked in the dark and unable to identify her attacker but police managed to retreive her attacker's DNA imprint - the equivalent of a unique genetic barcode - from her clothing.

Six months on, the public prosecutor in the area, Isabelle Pagenelle, decided to order mass DNA tests, which are due to be completed by mid-week, with test results expected in a month.

"The operation began calmly at 8 a.m.," Anne-Sophie Guilbot, a spokeswoman for the Fenelon-Notre-Dame school, told Reuters.

Mass testing of the kind is rare even if DNA-checking has become far more widely used since it emerged in the late 1990s that police might have been able to nab serial rapist and killer Guy Georges earlier had they matched a DNA sample he had given before several further killings.