Another unnamed 16-year-old boy was arrested at the scene on suspicion of murder and has been released on bail.
According to the US Sun, a woman named Maissa wrote on the London Crime Facebook Group: "I was there and saw the child. It was a painful thing. I do not think I will forget what happened for the rest of my life."
"The poor person was dying and people were celebrating as if the child was an animal," she added. "I am now in a state of shock from the ugliness of what I saw... could not stay there or celebrate."
Primrose Hill is a popular gathering site for Londoners wanting to see the New Year's Eve fireworks displays. It has also been described as a "playground for the rich and famous," with celebrities such as Kate Moss, Jamie Oliver, and Jude Law living nearby.
However since the pandemic, it has been known as a "party hotspot" equipped with drugs and alcohol. One anonymous local stated the stabbing was "tragic but inevitable" and reported he had made "hundreds" of complaints to police about people exhibiting shady behavior in the area.
Another resident, Gina Germano, said she had warned her two teenage boys about gang violence in the area before they embarked on their journey to the celebration.
A friend of the family said: "Harry had gone to Primrose Hill with a few friends to see the fireworks.
"The police haven't told the family too much yet. We don't know if Harry knew the man who was arrested, and we aren't clear on what happened, if there was an argument or a fight."
"His mother is devastated, the whole family are."
Another local resident told the Daily Mail that his son was there and recounted the eeriness of the incident to him:"A young lad had been stabbed and was lying on the floor. There were too many people to clear away completely so the officers had to tape off a small patch where the boy had fallen.
"Those officers and paramedics then worked on him, trying to save his life, basically as fireworks were being let off and people were whooping and hollering.
"It was a strange, eerie scene and a damning indictment on the knife violence gripping London.
"This wasn't a small event, there must have been around 30,000 people on the hill at that time last night.
"It's always been busy up there on New Year's Eve but last night was as packed as I'd ever seen it.
"This young lad was murdered in clear view of people."
Detective Chief Inspector Geoff Grogan, who is leading the investigation, said: "My thoughts and sympathies are with Harry's family and friends at this difficult time. He was a young man with the rest of his life ahead of him.
"His family are understandably devastated and specially trained officers are supporting them as they come to terms with their loss.
"A dedicated team of detectives are working hard to establish the events that led to such a senseless act of violence. We are reviewing CCTV footage from the area and are carrying out a forensic examination of the scene.
"We know Harry was with a group of friends near the viewing platform on Primrose Hill where they had gathered to celebrate the New Year. It is here where we believe Harry became involved in an altercation with devastating consequences.
"Primrose Hill was very busy at the time and I believe there are people who witnessed the incident who have not yet spoken to police.
"It is vital that we build a clear picture of the moments leading up to, and immediately after, Harry's murder and I need anyone with information about the altercation, or the attack, to contact us immediately."
