A young schoolgirl was raped during the night in her own bedroom by a stranger, police have revealed.
Police said the inquiry would be slow because of the age of the victim
The child, aged under 10 years, was attacked after the man sneaked into her home in Basildon, Essex.
Officers are interviewing five other children and the girl's mother, who were in the house at the time.
Detectives described the rape, which happened between Wednesday night and Thursday morning, as horrendous and said it was every parent's nightmare.
Forensic scientists are examining examples of material taken from the home in the hope of discovering the attacker's DNA, said police on Friday.
The little girl - whose exact age and identity cannot be given for legal reasons - has given police a description of the man who attacked her.
He is described as a black man, aged 18 to 20, with dirty teeth, one of them being distinctively clean.
He was skinny and had a grey top and loose ripped trousers, with a loop of chain down one side.
On Friday, Chief Insp Graham Carey: "We are investigating a stranger rape of a schoolgirl under the age of 10 in her Basildon home.
"It is an horrendous incident for the family and for the victim and it is every parent's nightmare."
He said the investigation would be slow and painstaking because of the age of the victim and the ages of other potential witnesses in the house.
Detectives say the child told her mother of the attack early on Thursday morning.
Police could find no obvious signs of a forced entry to the house and believe the attacker may have crept in an out unnoticed by the girl's mother and the other children.
Chief Insp Carey said: "In the house on Wednesday night was one woman - the victim's mother - and six children under the age of 10.
"Four of the children were the woman's, two were guests at the house and there was a mixture of girls and boys.
"As we have a unique situation with the location of the attack being the family home we will not, for legal reasons, be releasing the exact age of the girl.
"I would appeal to the attacker to come forward now before things get any worse.
"Extra officers will be patrolling and I would want to stress that this is an extremely unusual and rare incident which we are committing large numbers of resources to."