A 52-year-old schoolteacher accused of sexually abusing a schoolgirl for eight years has been arrested in Nakhon Sawan province.

Police arrested Nimit Khonpraneet outside a restaurant on Wednesday morning.

The victim, now 21, filed a complaint with police after Mr Nimit used footage of sexual acts to blackmail her, police said.

A police investigation found the sexual abuse occurred when the victim was a Mathayom 2 (Grade 8) student. The girl was experiencing a difficult time after her mother was killed in a road accident. She was living with her grandmother.

According to police, Mr Nimit, who taught physical education at the same Kamphaeng Phet school, offered to help take care of her and her grandmother. He told the girl to call him father. After gaining her trust, he lured her into his house, where he sexually abused her and took video of the acts. He told her not to tell others.

Using the footage to blackmail the student, he had sexually abused her for almost eight years. Once she got pregnant, he took her for an abortion, police said.

After the victim moved to stay with her aunt in Bangkok in October last year, Mr Nimit tried to contact her.

In January this year, he learned that she would come to visit her relatives in Kamphaeng Phet. After meeting her, he threatened her with a knife, coerced her into sex, and took video of the incident.

Mr Nimit told her that he would share their sex video clips if she refused to return to Kamphaeng Phet, police said.

The victim finally decided to tell her relatives about Mr Nimit. They later filed the complaint with police.