Hundreds of Taiwanese rallied on Sunday to show support for retaining the death penalty, after the beheading of a child in a street attack shocked the island.

Demonstrators dressed in black and held white roses in mourning for the four-year-old girl murdered on March 28 near a Taipei metro station. Many wore stickers reading "Death penalty is necessary."

The girl's mother tried to stop the attacker but was pushed away. Several bystanders were also unable to stop the man, who decapitated the child with a kitchen knife.

Police said the 33-year-old had previously been arrested for drug-related crimes and had sought treatment for mental illness. He was attacked by an angry mob while in custody.

The killing came less than a year after the throat of an eight-year-old girl was slit in her school restroom in Taipei. It sparked widespread public anger and fresh debate about capital punishment.

Taiwan resumed capital punishment in 2010 after a five-year hiatus. But executions are reserved for the most serious crimes such as aggravated murder and kidnapping.

Some politicians and rights groups have called for its abolition, but various opinion surveys show majority support for the death penalty.

"Taiwan is not safe, so death sentences are needed to deter crimes and they should be carried out. I hope this will make our society safer for all children," said office worker Chen Pei-chi, who took her sons aged three and six to the Taipei rally.

"I am really sad and angry that these random murders of children keep happening. All child-killers should be sentenced to death for hurting defenceless children and destroying their families, as losing a child is unbearable," said housewife Wu Chiu-mei, who has a three-year-old grandson.

In 2012 the murder of a 10-year-old boy in a playground reignited debate over the death penalty, after the suspect reportedly said he was anticipating free board and lodging in jail and would get a life sentence at most even if he were to kill two or three people.