More than 100,000 South Koreans are demanding the dismissal of a judge who reduced the prison sentence of a child rapist to three years.

Lee, identified only by his surname, was jailed in November for eight years for raping a 10-year-old child after making her drink an alcoholic beverage at his house in 2018.

The 35-year-old, who runs a private tutoring company, claimed the sex was "consensual" and that he believed the victim was much older than South Korea's age of consent, which is 13.

Last week, Seoul high court judge Han Kyu-hyun reduced the sentence to three years, saying there was "insufficient evidence" - other than the child's testimony - that Lee assaulted her.

Women's rights activists and the public protested the verdict, saying child victims of sexual violence were not being protected.

"The victim was a 10-year-old, and it seems like the appeals court treated the case as if she were an adult," said Chun Jung-ah, a lawyer who has represented many victims of sexual assault.

By Thursday more than 115,000 South Koreans signed the online petition calling for Han to be dismissed.