The trial of a French surgeon who for years sexually abused hundreds of patients, most of them minors, enters its final phase on Monday with the accused's lawyers set to make their closing arguments.

Joel Le Scouarnec, 74, has admitted to sexually assaulting or raping 299 patients in hospitals in western France between 1989 and 2014, many while they were under anaesthesia or waking up after operations. Of those patients, 256 were aged under 15 at the time.

The prosecution on Friday requested the maximum 20-year sentence for the former surgeon and also made the rare demand that he should be held in a centre for treatment and supervision even after any release.

"You were the devil and he sometimes is dressed in a white coat," prosecutor Stephane Kellenberger told Le Scouarnec, adding that an additional trial could be required to cover the cases of further victims whose abuse is not part of the current case.