The message was simple but heartfelt, it read: "To a wonderful girl you will be sadly missed, never forgotten."

It was one of dozens of messages among flowers and cards left by devastated schoolfriends of teenager Aimee Wellock at the place where she died.

From mid-afternoon yesterday, flowers had begun to arrive at the scene. Friends in uniform came straight from Parkside School which the 15-year-old had attended. Mothers and neighbours came carrying bouquets.

Five girls, still wearing their uniforms, walked with linked arms to the roped-off area overlooking Chellow Dean.

Too distraught to speak, the five shared several minutes of silence shedding tears and sharing hugs in their grief.

Aimee Wellock had been found unconscious, just yards from her home in Canford Drive, Allerton, following a "violent altercation" with a group of youths on nearby Chellow Dene on Tuesday evening.

Aimee had been with friends at about 8.20pm on Tuesday when a fight began.

A few minutes later she walked a short distance and collapsed unconscious.

Despite the extensive efforts by paramedics to revive her, she was pronounced dead at Bradford Royal Infirmary at 9.45pm.

Detectives are treating her death as suspicious.

Four teenagers - a 15-year-old boy and three girls aged 15, 17 and 19 - were arrested yesterday and are still being questioned by detectives investigating the incident

Aimee's parents Alan and Jackie Wellock and brother, James Wellock, 19, have spoken of their devastation and loss at Aimee's death in a statement released by police.

They said: "We are feeling absolutely devastated and at a complete loss.

"Aimee was a typical teenager, full of life and vitality. She loved dancing and had attended dance classes since she was eight years old. She was due to start her GCSEs in September and after that she wanted to go to dance college."

Police said the area would have busy on Tuesday evening and have appealed for witnesses to come forward.

"It was a warm evening and there was likely to be a number of people in the area," a spokesman said.

Friends and neighbours were today still shocked by the sudden tragedy in the middle of an area popular with dog walkers and playing children.

One woman who helped Aimee with her reading when she was at Allerton Primary School said: "Aimee was always full of life.

"She was a bright, bouncy little girl. I feel so shocked and so sad."

Another neighbour, Steve Stanworth, said his daughter Katy had gone very quiet after hearing of her friend's death.

He said: "It's such terrible news. Aimee was a polite, lovely girl. She did have her problems, she had eczema but she was getting help from the hospital for that."

One of Aimee's friends from school, Sarah Pekovic, who is 15 and in the year above, said everyone was very sad at school as news spread of Aimee's death.

She said: "No-one could believe it. People were saying that she'd been beaten up over a cigarette but it just doesn't make sense because she didn't smoke. She was popular, had lots of friends and was really lively and hard-working at lessons."

Several residents said the area had been plagued by youths, many riding on "beat-up" motorcycles, suggesting Aimee could have been hit by a bike.

Others suggested Aimee had been attacked by a gang of yobs.

Police said there was no suggestion "at the moment" that a quad bike was involved but that they believed there had been a "violent" altercation between two groups of youths.

A West Yorkshire Police spokesman said the violent altercation was believed to have been a physical one involving two groups of youths, male and female.

But he added: "A post-mortem has revealed Aimee had a serious medical condition but the cause of her death is not yet known." The spokesman said they were still awaiting results from medical tests.

"We are still unsure as to what part the altercation played in her death."

Resident Mark Tympalski said: "The field is a magnet for kids. It's a draw because it's such a wide open space.

"People will be very upset about what's happened. Many have children round here."

Sarah Pekovic, 15, who took the bus to school with her every day, said: "Everyone was in tears and crying. She was a lovely girl, she was funny and lively. She worked hard at school."

"She wouldn't put up a fight, she would walk away. She didn't deserve this. She was a great friend - someone you could rely on."

Jessica Webster, 15, was in Aimee's year at Parkside school in Cullingworth.

"The last time I saw Aimee was on Tuesday at school and she seemed really happy.

"She was a really nice girl who always put others first and she was always asking people if they were okay and if she could do anything to help anyone she would.

"We are all very upset by what has happened, everyone is talking about it."