Four boys – aged 13, two aged 14 and one aged 15 – have been arrested on suspicion of murder.
Police believe that Ava and her friends had had a verbal argument, which led to Ava being assaulted, and the offenders then running away.
Merseyside Police previously said that she had been stabbed but later said that a post-mortem explanation would be carried out to establish the cause of her death.
Police officers were called at 8:39pm to reports of an assault. When they arrived they discovered that Ava, who had been with friends, was collapsed on the ground.
A member of the public who witnessed the incident was giving her first aid.
Paramedics tried to help Ava and took her to Alder Hey Children’s hospital, but she sadly died a short time later.
The city centre was busy at the time because the Christmas lights had just been officially switched on. The police are appealing to anyone who saw the incident, or who may have captured it on their mobile phone, to come forward.
Mary Katilius, 65, said that she had been in Liverpool city centre with her 18-year-old granddaughter when Ava White was attacked. “We heard screams and someone said to call an ambulance. My granddaughter said she saw some young guys running off. We rushed over straight away but there was already a man helping her.”
Peter Duffy, headteacher of Notre Dame Catholic College, where Ava White was in Year 8, said: “Ava was a much-loved, valued and unique member of the Notre Dame family.”
He described her as an “incredibly popular girl with a fantastic group of friends.”
Assistant mayor of Liverpool Sarah Doyle also paid tribute to Ava on Friday, saying she was “heartbroken” to hear the young girl had died.
“I know news of this tragedy will shake communities across our city,” she said. “My thoughts are with Ava’s family, friends and school.”
Assistant Chief Constable Jon Roy said: “Our thoughts and condolences go out to Ava’s family, who are being supported by specialist Family Liaison officers. Their world has been torn apart and no parent should ever have to face that knock on the door from police officers to say that their child has died.”
He added: “Ava’s death should be a reminder to us all about the part that we each have to play in eliminating violence against women and girls.”