A 16-year-old girl was stabbed over 20 times and bludgeoned to death by a youth in a busy bylane as passersby looked on in northwest Delhi's Shahbad Dairy area - an incident that has drawn massive outrage as the video of the horrific killing appeared online.

Delhi Police said the accused, 20-year-old Sahil, was arrested from Bulandshahr in Uttar Pradesh on Monday.

He and the victim, Sakshi, were in a "relationship" but had a quarrel on Saturday. The victim had gone shopping on Sunday evening for the birthday party of her friend's child when she was accosted by the accused in the densely populated neighbourhood, they said.

A nearly 90-second video of the incident that was shared online showed the accused pinning the victim to a wall with one hand and stabbing her repeatedly. He did not stop even when the girl slumped to the ground, jabbing the knife into her over 20 times, kicking her and then slamming a cement slab on her repeatedly.

In a shocking display of public apathy, people can be seen passing by, with some bystanders staring in alarm, but not doing anything to stop the brutal attack.

The accused is seen walking away from the victim in a casual manner only to turn back and again hit her with the slab before leaving the site.

"I have never seen such a frightening case. What was the fault of the 16-year-old girl that she was brutally killed on the road? Several people saw this but did not pay heed. No one is afraid of the police and the law in Delhi," Delhi Commission for Women Chairperson Swati Maliwal said.

Delhi Chief Minister Arvind Kejriwal and other AAP leaders attacked Lieutenant Governor V K Saxena, saying it was his responsibility to maintain law and order in the city, while the Delhi BJP claimed it was a case of "love jihad", and slammed the AAP for "trying to portray" it as an "ordinary" murder and a law and order issue.

Calling the incident "extremely disturbing and appalling", the National Commission for Women said its Chairperson Rekha Sharma has written to the Commissioner of Police to conduct a fair and time-bound investigation in the matter.

The Commission has formed a three-member team headed by member Delina Khongdup to look into the matter." Delhi Police PRO Suman Nalwa said the accused Sahil worked as a fridge and AC mechanic. He lived in a rented accommodation with his parents and three siblings in Shahbad Dairy area.

A case under Section 302 (murder) of the Indian Penal Code has been registered at Shahbad Dairy police station on the complaint by the victim's father, the police added.

The police suspect that "strained relationship" of the accused with Sakshi could be a possible reason behind the crime.

A police officer said that the girl's skull was ruptured, citing preliminary findings of the post-mortem.

Sakshi, whose father is a labourer, passed Class 10 this year. The victim's parents, who are residents of JJ Colony in Shahbad Dairy and have a younger son, said she was staying with her friend Neetu for the last 15 days since the latter's husband was out of Delhi for work.

Recalling Sunday's event, Neetu, who has two children, said Sakshi was busy organising the birthday party for her daughter and went to the nearby market to get a dress for the child.

She informed Neetu that she wanted to use the washroom and was going to their common friend's place.

Neetu claimed that Sakshi and Sahil often fought with each other but she got to know about their "friendship" only six months ago.

Seeking justice for their daughter, Sakshi's parents demanded capital punishment for the accused.

They said neither she nor her friends had told them about Sahil.

The victim's father said that the police have assured them that they would get justice for their daughter.

"We believe and trust the police when they said they will help us in getting justice for our daughter," he said.

Sakshi's mother said he had last spoken to her on Sunday afternoon.

"My daughter had been staying with Neetu and her two children for the past 15 days. I had spoken to my daughter around 1:30 pm and she had told me that she will return home once Neetu's husband is back," she said.

Many took to social media to express anger over the brutal assault and the "insensitivity" shown by people who did nothing to save the victim.

"A minor girl was brutally murdered in Delhi. This is very sad and unfortunate. The criminals have become fearless, there is no fear of the police. LG sir, law and order is your responsibility, do something," Chief Minister Arvind Kejriwal said.

In a statement, Delhi BJP president Virendra Sachdeva said the case should be tried in a fast-track court.

Sachdeva claimed locals had informed him that the accused was harassing the minor girl for "a long time".

It is "regrettable" that the Chief Minister of Delhi was "trying to portray" the "brutal killing" of a Hindu girl as a law and order issue, whereas it is a case of "Love jihad", Sachdeva said.

"The red Kalawa (sacred thread) tied on the hand of arrested Sahil Sarfaraz clearly showed that he is a member of Love Jihad gang working in a well-planned manner," Sachdeva charged in his statement.

"Love jihad" is a term often used by BJP leaders and right-wing activists to allege a ploy by Muslim men to lure Hindu women into religious conversion through marriage.

Except for the headline, this story has not been edited by The Telegraph Online staff and has been published from a syndicated feed.