A group of 20 South Korean lawmakers introduced a bill Wednesday that would allow for the physical castration of repeat sex offenders, amid public outrage at a spate of brutal sex crimes.

If the bill is adopted, courts could order the testicular castration of recidivist sex offenders who fail to respond to behavioural or chemical treatment.

Under legislation adopted by South Korea's parliament in 2010, chemical castration can be carried out on serial sex offenders convicted of crimes against minors aged under 16.

In May this year, a 45-year-old man became the first to undergo the chemical castration process which involves receiving injections to alter hormone levels.

But lawmaker Park In-Sook, a medical doctor and one of the 20 MPs behind the bill introduced on Wednesday, said the effects of such medication were reversible as sexual impulses often return strongly when treatment ends.

"We must take more drastic measures such as physical castration in order to stem mounting sex crimes," she told journalists.

Her aide, Park Jong-Won, said the bill would need to pass through several parliamentary committees before being subjected to a vote by a full session of the National Assembly.

But he suggested there was a "high possibility" that it could eventually secure a simple majority in the 300-member house.

The government is under mounting pressure to introduce tougher anti-sex crime measures following a series of high-profile cases.

President Lee Myung-Bak was forced to issue a public apology on behalf of the government in August after the brutal rape of a seven-year-old girl abducted from her home prompted a public outcry.

Police have arrested a man in his early 20s in the case.

In another case last month, a convicted sex offender wearing an electronic tracking device, stabbed a man to death and badly wounded four others at a bar as he attempted to rape a woman.