Girls as young as 11 "expect" to have to perform sex acts on rows of boys for up to two hours at a time in parts of London, a watchdog said in a warning that serious child abuse is rife right across England.
Deputy Children's Commissioner Sue Berelowitz said her in-depth study of the problem suggested there "isn't a town, village or hamlet in which children are not being sexually exploited".
And she shocked MPs with a graphic description of just some of the crimes she had encountered in her research for a major report due out in September.
Giving evidence to the Commons home affairs committee, Ms Berelowitz said the recent sex abuse case in Rochdale - which involved mostly men of Pakistani origin and white girls - was just one part of a wider picture of exploitation involving victims and abusers of all races and cultures.
"What I am uncovering is that sexual exploitation of children is happening all over the country," she told the cross-party committee.
"As one police officer who was the lead in a very big investigation in a very lovely, leafy, rural part of the country said to me: 'there isn't a town, village or hamlet in which children are not being sexually exploited.
"The evidence that has come to the fore during the course of my inquiry is that that, unfortunately, appears to be the case.
"We should start from the assumption that children are being sexually exploited right the way across the country.
"In urban, rural and metropolitan areas, I have hard evidence of children being sexually exploited. That is part of what is going on in some parts of our country. It is very sadistic, it is very violent it is very ugly."
Giving examples from the capital, she said: "There are parts of London where certainly children expect to have to perform oral sex on line-ups of boys, up to two hours at a time from the age of 11.
And it was "quite common" for girls to be lured via internet chat rooms to meet a friend, only to be met by a group of boys and gang raped in a park.
"Then another group of boys come, they take her to another part of the park and she is serially raped again.
"I wish I could say to you that such things are uncommon but I'm afraid they are quite common."
In the Rochdale case, nine men, mainly of Pakistani origin, were found guilty of plying girls as young as 13 with drink and drugs so they could use them for sex.
"I regret to say that there are parts of every single community - white, Pakistani, Afghan, Gypsy and Romany travellers, you name it - who are seeing children as easy access in terms of sexual exploitation. And in terms of victims we are seeing the same sort of profile."
Ethnic minority victims were "too often missed out".
The deputy commissioner told the visibly-stunned MPs that "what is being done is so terrible that people need to lay aside their denial" or risk victims being disbelieved.
Victims numbered in the thousands not the hundreds, she said, pledging that the full scale would be set out in her report in September.
She said she was "extremely concerned" about the role being played by the internet in enabling and fuelling abuse, and ridiculed the idea that parents could prevent access.
Young people were acting out scenes they saw in online pornography and even organising abuse via social networking sites and messaging systems, she said.
In one case, boys aged 14 and 15 were "summoned" via BlackBerry Messenger to the gang rape of a "very, very young girl" which lasted several days.
"Boys were being called while some were raping the girl to say 'come, come, come, you can join in too' and they were arriving and elbowing each other out of the way to rape her."
One police force showed her a list of more than 1,000 girls aged between 12 and 14 whom a man in his 40s masquerading as a boy had managed to make his "friends" on Facebook.
"We have gathered quite a lot of evidence to show that there is no doubt that social networking sites can be a source of real problems for this," she said.
She said easy access to extreme pornography was a particular concern.
"We've had boys say to us - some of the boys I've spoken to who've been involved in sexual exploitation - 'it was like being in a porn movie'.
"They have watched things and then they've enacted them.
"Parents may think they can control what's going on because they can have a blockage on the computer but the reality is children can get anything they like on their mobile phones.
"And they are.
"It has definitely affected children's thresholds of what they think is normal."
In another case, older men were using young male gang members as a "front line" in a wider abuse network, and had even forced two of the boys to have sex and filmed it on a mobile phone to ensure their compliance.
Speaking about the race issue, she told the committee she had visited a "racist" estate in the north of England where there was routine sexual abuse of children within an all-white community.
"I have been to gang-associated areas in the north of England.
"I am thinking of one particular estate which is exclusively white, because it is such a racist estate, where there is a very strong and identified pattern of the white males on that estate sexually exploiting the white females on that estate.
"So it is really important to hold all of it in mind."