A woman cut off her husband's penis with a pair of scissors and threw the severed member into a river in revenge for his affair with another woman and his physical abuse, police in Taiwan say.

The 30-year-old Vietnamese woman, identified only by her surname, Pan, cut off about half her husband's penis at their home in the southern city of Tainan after he took drugs and sleeping pills and fell asleep, police said on Sunday.

The woman allegedly claimed she had thrown the severed member of her drug-addicted Taiwanese husband into a river before turning herself in.

"She has been taken into custody on charges of assault," a police officer said on condition of anonymity.

The woman allegedly told police she felt no regret about what she had done to her husband, who is 29-years-old, jobless and a known user of illegal drugs.