She was found wandering half-naked and in shock in Felmores Park at Pitsea.
Women detectives were trying to coax details of the rape from her last night at Basildon police station.
She told police that her attacker was black, aged between 20 and 30, of medium height, with protruding front teeth and wearing dark clothes.
Superintendent Ivan Dibley, leading the hunt for the child's attacker, said: 'It was a horrific attack. We are all very shocked by what has happened. The little girl is obviously very distressed by her ordeal.
'I would like to urge anyone who may be able to help catch her attacker to come forward as a matter of urgency.
'With an attack of such a serious nature I must warn parents of young children not to allow them to go unsupervised in that park.'
The girl went to the park to meet a friend with a dog, but was grabbed before her playmate arrived.
In a separate case, police were hunting a rapist who attacked a 73-year-old woman in her home yesterday.
Detectives are waiting to get more details from the widow, who was recovering in hospital after the attack at Horfield, Bristol.
Police and tracker dogs were scouring the area. Chief Inspector Colin Benson, a spokesman for Avon and Somerset Police, said that the woman opened her door to the man at about 1am believing he was a neighbour in need of help.
'She is the kind of lady who sees nothing but good in people. But after an act of kindness she was subjected to a really vicious and nasty attack.
'My officers have been sickened by this unprovoked assault on a defenceless woman.'
The attacker, who apparently called himself 'Mark', forced his way into the hallway and immediately attacked her.
She later required stitches to a head wound and police believe her attacker could have bloodstains on his clothing.
The attacker was white, 5ft 10in (1.77m) tall and slim. He had short cropped hair and was wearing a white shirt or T-shirt and jeans. He had a small coin on a gold chain around his neck and a ring on one hand.
Detective Chief Inspector Bill Davies, who is leading the hunt, said the victim's injuries included a fractured jaw.Reuse content