A retired French surgeon has been sentenced to 15 years in jail at the end of his closed-doors trial for the rape and sexual abuse of four children in the first part of France's biggest ever paedophilia case.

Joel Le Scouarnec, 70, remained impassive as the verdict was read out on Thursday at the court in Saintes, western France, keeping his arms crossed without a glance at his victims, who embraced each other, overcome with emotion.

Le Scouarnec, who could have faced 20 years behind bars after being found guilty on all charges, will also be subject to a three-year supervision order at the end of his sentence. He has 10 days to appeal.

Judge Isabelle Fachaux said that despite a 2005 conviction for viewing child pornography, Le Scouarnec had continued to offend, making a lengthy jail term necessary.

"We are really satisfied... it's a fair sentence," said Francesca Satta, the lawyer for one of the victims, who had reported Le Scouarnec in 2017.

In his final words to the court, Le Scouarnec said he did not expect leniency, according to lawyers present at the trial, which was held behind closed doors at the victims' request.

"I do not ask for forgiveness or compassion... only the right to become a better man again," he was quoted as saying.

"He explained that he had a lot of regrets... without necessarily asking for an apology. He knows that what he did is unforgivable," his lawyer Thibaut Kurzawa said.

The once-respected doctor and father of three sons now faces a possible second trial involving hundreds of cases of sexual assault or rape.

Le Scouarnec was charged in 2017 after testimony from one of his victims, his neighbour's six-year-old daughter. 

The investigation quickly uncovered three others -- two of his nieces, raped between 1989 and 1999, and a hospital patient who was only four in 1993.

Prosecutors say searches of Le Scouarnec's home uncovered archives detailing sexual assaults or rapes of as many as 312 victims, both adults and children, starting in 1986 while he worked at hospitals in central and western France.

Police found more than 300,000 indecent images of minors, including pictures of his two nieces.

Le Scouarnec admitted assaulting the four children but initially denied the rape charges.

During the trial, which started on Monday, Le Scouarnec admitted having raped his nieces, now aged 35 and 30. His admission "did them a lot of good", according to their lawyer Delphine Driguez.