A man suspected of decapitating a four-year old girl was beaten by an angry mob as he was detained in Taiwan, with parliament saying it would introduce tougher sentences for child-killers.

The victim, Liu, was with her mother as she cycled to a metro station in Taipei to meet relatives, when the killer grabbed the child from behind.

Pushing away the mother, who had rushed forward to save her daughter, he beheaded the child with a kitchen knife.

The suspect, surnamed Wang, had been booked in the past over drug-related crimes. He was unemployed and living with his parents and had been hospitalized due to mental health issues, according to the police.