A music teacher at a well-known public school in Bangkok has admitted sexually abusing a 15-year-old student for almost two years after more than 100 video clips of the abuse were found on his phone.

The boy's mother said she learned about the abuse from her son last Thursday.

She said her son had been subjected to sexual abuse at the hands of the music teacher for almost two years. The teacher also threatened him not to tell anyone about it.

The boy's mother said the teacher recently became more abusive, adding that he usually persuaded her to have her son take special tutorial classes.

The school director promised to launch an investigation lasting seven months. The parents said this would take too long so they contacted the Sai Mai Tong Rod Facebook page for help instead.

The page founder said he would contact the deputy education minister and urge him to take action against the music teacher.

Police said the teacher admitted to the crime after the video clips were found on his mobile phone. None of the clips had been shared online.