A SIX-year-old boy allegedly killed a premature newborn baby after dropping her on the floor.

A criminal investigation has been launched after the horror unfolded at the Jeanne-de-Flandre Children’s Hospital in Lille.

A baby identified as Zayneb-Cassandra was declared 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”.

It comes after a Brit boy, eight, was left with brain injuries after a tragic Ibiza hotel plunge.

He was trying to get a towel from the balcony, it emerged.

The young boy also suffered a skull fracture and broken jaw in Tuesday night’s fall, and was with his grandma at the time.