A newborn baby has died after reportedly being thrown 40ft from a window by her five-year-old sister.

The tragedy came as the pair were left home alone by their mother while her husband was at work, say law enforcement.

Passersby heard a girl screaming from a fourth-floor window, then saw the motionless baby on the ground.

Witnesses said their ‘knees went weak’ at the horrific sight.

Paramedics confirmed the 21-day-old’s death at the scene after falling onto concrete from a residential building in Vasilyevo village,Rusia.

‘A criminal case has been opened over the death of the infant,’ said the Russian Investigative Committee.

Their mother now faces prison.

Investigators are examining whether the five-year-old was ‘jealous’ of the new baby, and the mother’s motive for leaving her daughters home alone.

One report said she was visiting a friend.

‘The actions of the parents who left the children unattended, as well as other possible scenarios, are being investigated.’

A report citing local sources said: ‘The girl was upset that there was another child in the flat, and out of jealousy, she threw the infant out of the window.’

District chief in Zelenodolsk, Tatarstan, Mikhail Afanasyev, said: ‘Law enforcement officers are now investigating the situation.

‘I express my condolences to the family of the deceased and urge all parents to be vigilant and never leave your children alone.’