A tragic incident occurred involving a six-year-old boy who is said to have accidentally caused the death of a premature newborn baby by dropping her on the floor.

This has prompted a criminal investigation after the unfortunate event took place at the Jeanne-de-Flandre Children’s Hospital in Lille.

The newborn, named Zayneb-Cassandra, was pronounced dead yesterday.

She suffered a traumatic brain injury last Friday after allegedly being dropped on the floor by the boy.

He was found alone with the unconscious baby in a neonatal unit.

The boy, described as a “disruptive presence”, was spotted wandering around the hospital unattended.

Investigators said he “treated the baby like a doll”.

The baby was her mother’s first child, who was born premature at seven and a half months to a 23-year-old mum.

Zayneb-Cassandra’s grandmother told the Voix du Nord newspaper: “The boy would arrive at 7am and spend all day running up and down the hallways.

“All the mothers were complaining, and a nurse even warned the child’s mother that there was a problem. He was entering the other rooms.

“He also entered Zayneb’s room for the first time. He said she looked like a doll, and my husband, who was there, took him out.”

Zayneb was found unresponsive on the floor, next to the six-year-old, who was in a chair.

“It seems he tried to grab her by her nappy, and she fell on her head,” said Zayneb’s grandmother.

The baby was rushed to intensive care – but was declared dead after suffering “a serious brain injury”.

An investigation has been opened by the juvenile unit of the Lille Judicial Police Service, in conjunction with local prosecutors.

A spokesman said: “Investigations are currently underway in this case.”

The hospital also announced the opening of “an internal administrative investigation”.